Nine species of the mirine plant bug genus Castanopsides Yasunaga from eastern Asia are revised. The majority of Castanopsides species appear to be oak-inhabitants. Four new species arc diagnosed and described: Castanopcides takaii sp. n. from Japan and Taiwan, and C. gotohi sp. n., C. montanus sp. n. and C. taiwanus sp. n. from Taiwan. New combinations of four species previously placed in Arbolygus Kerzhner are proposed: Castanopsides potanini (Reuter) comb. n., C. dasypterus (Reuter) comb. n., C. kerzhneri (Kerzhner) comb. n. and C. falkovitshi (Kerzhner) comb. n. All previously described taxa are diagnosed and redescribed, and a key is provided to distinguish the species. The zoogeography and phylogeny of the Castanopsides species are discussed.