The taxonomy of Rhinolophus yunanensis Dobson, 1872 (Chiroptera: Rhinolophidae) is revised by reference to specimens collected from the provinces of Sichuan and Yunnan, China, and from Thailand. The Thai specimens are found to differ from the Chinese ones in external and cranial morphology and karyotype, and it is thus concluded that what has hitherto been R. yunanensis actually represents two distinct species, including a new one. The new species is described on the basis of 10 specimens collected from Chiang Mai, Thailand. It is the largest species of the pearsoni group of the genus, with a large skull and long ears. Rhinolophus yunanensis is redescribed on the basis of specimens collected from China. In Principal Component Analyses of the cranial morphometric data, the new species was completely separated from the redescribed R. yunanensis and R. pearsoni.