Liangdang County (simplified Chinese: 两当县; traditional Chinese: 兩當縣; pinyin: Liǎngdāng Xiàn) is a county under the administration of Longnan City, in the southeast of Gansu Province of China.

It has a land area of 1,374 km2 (531 sq mi), and a population of 50,000 in 2004.

The county seat is located in Chengguan Town.

[1] Liangdang is best known in China for an April 1932 uprising launched by Xi Zhongxun, father of Xi Jinping.

[2] Liangdang County is divided to 6 towns and 6 townships.