Lohajang (; lit. rusting of iron) is an upazila of Munshiganj District in Dhaka Division, Bangladesh.
Lohajang is located at on the south bank of Padma River. It has a total area of 131.10 km<sup>2</sup>.
According to the 2022 Bangladeshi census, Louhajang Upazila had 43,497 households and a population of 177,802. 9.33% of the population were under 5 years of age. Louhajang had a literacy rate (age 7 and over) of 77.98%: 79.68% for males and 76.41% for females, and a sex ratio of 93.55 males for every 100 females. 21,422 (12.05%) lived in urban areas.
According to the 2011 Census of Bangladesh, Louhajang Upazila had 35,978 households and a population of 159,242. 33,395 (20.97%) inhabitants were under 10 years of age. Louhajang had a literacy rate (age 7 and over) of 56.22%, compared to the national average of 51.8%, and a sex ratio of 1009 females per 1000 males. 4,945 (3.11%) lived in urban areas.
Louhajang Upazila is divided into ten union parishads:
The union parishads are subdivided into 115 mauzas and 114 villages.