is a town located in Shiribeshi, Hokkaido, Japan.
As of 24 May 2020 the town had an estimated population of 2,739, and a density of 7.2 persons per km<sup>2</sup>. The total area of the town is 345.65 km<sup>2</sup>.
Kuromatsunai is located in the southern part of Shiribeshi Subprefecture and while close to both the Sea of Japan and the Pacific Ocean, the town itself has no coastline. The Shubuto River and Kuromatsunai River flow through Kuromatsunai.
The town, being the northernmost area of Japan in which beech trees grow naturally, has had the Fagus crenata, Japanese beech, tree designated a natural treasure. The area is known as the Kuromatsunai Depression because it is low lying compared to most of Hokkaido and is agriculturally intensive.