is a city in Miyazaki Prefecture, Japan. , the city had an estimated population of 47,872 in 21482 households, and a population density of 89 persons per kmò. The total area of the city is .
Nichinan is located in the southern part of Miyazaki Prefecture on Japan's southernmost main island, Kyà «shà «. It is surrounded by the Wanizuka mountain range on the north, east and south, and faces the Hyà «ga Sea to the east. Much of the city is within the borders of Nichinan Kaigan Quasi-National Park. Approximately 78% of the city's area is forest, much of which is occupied by the Obi cedar, a specialty tree. The Sakatanigawa River runs through the city from east to west. This river joins the Hiroto River near its mouth and flows into the Pacific Ocean.
Nichinan has a humid subtropical climate (Köppen climate classification Cfa) with hot, humid summers and cool winters. The average annual temperature in Nichinan is . The average annual rainfall is with June as the wettest month. The temperatures are highest on average in August, at around , and lowest in January, at around . The highest temperature ever recorded in Nichinan was on 2 August 2013; the coldest temperature ever recorded was on 24 January 1976.
Per Japanese census data, the population of Nichinan in 2020 is 50,848 people. Nichinan has been conducting censuses since 1920.
The area of Nichinan was part of ancient Hyà «ga Province. During the Sengoku period, the area was ruled by the Ità  clan based at Obi Castle and the site of numerous battles with the neighbouring Shimazu clan. The Shimazu clan had unified Satsuma Province and à Âsumi Province under its control, and began to clash with the Ità  in 1570. The Ità  were finally defeated by the Shimazu clan in 1578. After seeking help from the hegemon Toyotomi Hideyoshi, the family's lands were restored in 1587 after his invasion of Kyà «shà «. By the Edo period, the Ità  clan ruled as daimyà  of Obi Domain, and the present-day city borders roughly correspond to the holdings of the domain. The domain was noted for the quality of its han school, one of whose graduates was the Meiji period diplomat Marquis Komura Jutarà Â.
The town of Aburatsu and the villages of Agata, Obi, Hosoda, Nangà  and Tà Âgà  were established on May 1, 1889 with the creation of the modern municipalities system. Obi was raised to town status on January 1, 1900, followed by Nangà  on December 1, 1940, Hosoda on January 1, 1941 and Agata on May 3, 1950. On January 1, 1950, the city of Nichinan was established through an amalgamation of the towns of Agata, Aburatsu, and Obi, and the village of Tà Âgà Â. On February 1, 1955, Futo village and Hosoda town joined the city. On April 1, 1956, Nichinan absorbed Sakatani village, Kahara village, and the Odotsu district.
Since 1963, Nichinan has been the spring training location for the Hiroshima Carp baseball team.
In 1999, a 12-meter wharf was completed at the eastern head of Aburatsu port. Aburatsu's increasing role as a harbor has made it a regular stopover for both domestic and foreign ships, and it is becoming an authentic international trading port. From 2001 to 2010, a general plan for the future of Nichinan was drawn up, with the simple theme of progressing Nichinan as, "a city that combines its fragrant history and culture with the sunshine and lush green mountains."
During the nationwide round of Heisei-era mergers, the was formed in August 2004 by the area's residents to consider the merger of the three municipalities. The group was dissolved in May 2005 when the Kitagà  Town Council vetoed the proposed merger bill despite support for the merger by residents in both Kitagà  and Nangà  towns. The association was reconstituted on September 28, 2007, when merger supporters in both towns gained majorities on their respective town councils. On March 30, 2009, the three municipalities agreed to merge and become the new city of Nichinan.
On August 8, 2024 at 16:22 JST, the 7.1 2024 Hyà «ga-nada earthquake struck in the Hyà «ga Sea off the coast of Miyazaki Prefecture, Kyushu, Japan, northeast of Nichinan. Nichinan experienced seismic intensity of 6- on the Japan Meteorological Agency seismic intensity scale.
Nichinan has a mayor-council form of government with a directly elected mayor and a unicameral city council of 19 members. Nichinan contributes two members to the Miyazaki Prefectural Assembly. In terms of national politics, the city is part of the Miyazaki 1st district of the lower house of the Diet of Japan.
Agriculture, forestry and fisheries and the pillars of the local economy. Commercial fishing of bonito was designated as a Japanese agricultural heritage in 2021 and Katsuomeshi, a dish of bonito sashimi served with soy sauce, is a noted local dish. Mandarin oranges, ponkan, sweet peas, green peppers, kumquats, and rice are the main agricultural products of Nichinan.
Nichinan has 14 public elementary schools, seven public junior high schools and three combined elementary/middle schools operated by the city, and two public high schools operated by the Miyazaki Prefectural Board of Education. There is also one private junior high school and one private high school. The prefecture also operates one special education school for the handicapped.
There are seven kindergartens, 14 elementary schools, 11 junior high schools, and three high schools located within the city.
There are three major yearly festivals in Nichinan:
Other events include spring and autumn training for the Hiroshima Carp baseball team, swimming and marathon events, and monthly morning markets held at Aburatsu port and in front of Nichinan City Hall.
Other points of interest include: