A new fern species, Polystichum fengshanense, is described and illustrated from nine karst caves in northern Guangxi, China. It is a member of Polystichum sect. Haplopolystichum (Dryopteridaceae). A phylogenetic analysis based on chloroplast trnL-F sequences suggests that the new species is most closely related to P. cavernicola, P. minutissimum, and P. speluncicola, species described from karst caves in adjacent southern Guizhou. Morphologically, P. fengshanense can be easily distinguished from these three species by having narrow-type microscales on the abaxial laminar surface, sessile pinnae, and sori closer to the midrib. Palynologically P. fengshanense has granulate perispore sculpturing, whereas P. cavernicola has verrucate perispore sculpturing and P. speluncicola has cristate perispore sculpturing with numerous spinules. Polystichum fengshanense is considered to be critically endangered (CR) based on IUCN red list criteria because of its restricted distribution.