Abstract: The myrmicine ant genus Perissomyrmex M.R. Smith, 1947 is reviewed. Perissomyrmex emarginatus Ogata & Okido, 2007 is a junior synonym of P. bidentatus Zhou & Huang, 2006. Perissomyrmex nepalensis Radchenko, 2003 is a junior synonym of P. monticola De Andrade, 1993. A new species collected from Tibet, China, P. medogensis sp.n., is described. Descriptions of soldier and queen castes and measurements of worker caste of P. bidentatus are supplemented based on the specimens collected from Hengduan Mountains of southwestern China. Worker dimorphism is discovered in P. medogensis sp.n. and P. bidentatus in the Old World fauna. It implies that workers of the genus are weakly dimorphic. A key to the six known species of the genus of the world is provided based on the worker caste.