Inonotus hainanensis sp. nov., collected in the tropical forests of southern China, is described and illustrated. It forms abundant, thin, and imbricate pileate basidiocarps. Microscopically, the species is characterized by lacking both setal hyphae and hymenial setae, and ellipsoid, thick-walled, yellowish brown basidiospores. It might be related to I. tenuicarnis, both species sharing similar basidiospores and absence of hymenial setae and setal hyphae. The latter has a reddish brown crust on pileal surface, and its basidiocarps become very hard when dry. In addition, I. tenuicarnis has a glancing pore surface and its pores are slightly smaller.