A new porcellanid crab, Lissoporcellana demani n. sp. is described based on material from the Beibu Bay in the northern South China Sea. The new species can be distinguished from other congeners by the shape of rostrum, form of fixed finger of smaller cheliped and armature of lateral margins of carapace. The poorly known species L. streptochiroides (Johnson, 1970), which resembles L. demani n. sp. in carapace shape, is redescribed on the basis of examination of the syntypes from Singapore and transferred to Pisidia Leach, 1820.