Qin'an County (Chinese: 秦安县; pinyin: Qín'ān Xiàn) is an administrative district in Gansu, the People's Republic of China. It is one of 58 counties in Gansu, and administratively under Tianshui prefecture, with the city of the same name being the prefecture seat. Its postal code is 741600, and in 1999 its population was 567,553 people.
It is reputedly the county where Zhuge Liang's troops, commanded by Ma Su, were defeated by Zhang He at the Battle of Jieting.
Known as Chengji (成紀), it vied with Tianshui (then known as Shanggui) as the seat of the medieval province of Qinzhou during the Tang Dynasty and Five Dynasties eras.
Coordinates: 34°54′26″N 105°41′54″E / 34.9071°N 105.69833°E