The third species of the ant genus Perissomyrmex in the world, P. fissus sp. nov., is collected from Ailao Mountain Nature Reserve of Yunnan Province. Perissomyrmex is a new record genus in China. Taxonomic key based on worker caste is provided for the 3 species: P. snyderi Smith, P. monticola de Andrade, and P. fissus sp. nov.