| Kōsa | |
| Native Name Lang: | ja |
| Settlement Type: | Town |
| Seal Type: | Emblem |
| Pushpin Map: | Japan |
| Pushpin Map Caption: | Location in Japan |
| Coordinates: | 32.65°N 179°W |
| Subdivision Type: | Country |
| Subdivision Name: | Japan |
| Subdivision Type1: | Region |
| Subdivision Name1: | Kyushu |
| Subdivision Type2: | Prefecture |
| Subdivision Name2: | Kumamoto Prefecture |
| Subdivision Type3: | District |
| Subdivision Name3: | Kamimashiki |
| Extinct Title: | Now part of |
| Leader Title: | Mayor |
| Leader Title1: | Vice Mayor |
| Unit Pref: | Metric |
| Area Total Km2: | 57.87 |
| Population Total: | 10,924 |
| Population As Of: | February 28, 2017 |
| Population Density Km2: | auto |
| Timezone1: | JST |
| Utc Offset1: | +09:00 |
| Blank Name Sec1: | City hall address |
| Blank Name Sec2: | Climate |
| Blank Info Sec2: | Cfa |
is a town located in Kamimashiki District, Kumamoto Prefecture, Japan.
As of February 2017, the town has an estimated population of 10,924[1] and a density of 190 persons per km2. The total area is 57.87 km2.
Kōsa has a humid subtropical climate (Köppen climate classification Cfa) with hot, humid summers and cool winters. There is significant precipitation throughout the year, especially during June and July. The average annual temperature in Kōsa 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 Kōsa was on 14 August 2018; the coldest temperature ever recorded was on 25 January 2016.
Per Japanese census data, the population of Kōsa in 2020 is 10,132 people. Kōsa has been conducting censuses since 1920.
Since its inception in 1983, the Kumamoto Kōsa 10-Miler road race has seen several top rated achievements being set during the event, which is run in December. The most recent new world record for the 10 miles was set in December 2022 by Bernard Koech.