A new fern species, Pteris xiaoyingae (sect. Pteris, Pteridaceae), is described from a karst cave in southern Guizhou, China. The new species is a small-sized limestone rock-dwelling plant. It has trifoliate leaves with two lateral pinnae each mostly divided at the base into two almost free basiscopic lobes. Morphologically it is similar to P. gallinopes and P. deltodon that also occur on shady limestone walls often inside or near karst caves. Pteris xiaoyingae differs from P. gallinopes in its middle pinna being ovate-lanceolate with blunt apex and lateral pinnae and their lobes oblong-obovate with round or obtuse apex. Pteris xiaoyingae also has wider pinnae (more than 7 mm) than P. gallinopes (2–4 mm). Pteris xiaoyingae is distinguishable from P. deltodon by being smaller in stature (only 4–7 cm high in P. xiaoyingae vs. 10–40 cm high in P. deltodon) and by having lamina more or less pedate in outline (for the majority of leaves with lobed lateral pinnae) and pinnae and lobes with round or blunt apices (vs. with short or long acuminate apices in P. deltodon). Palynologically, P. xiaoyingae has conic-deltate spores with verrucate sculpture while both P. gallinopes and P. deltodon have deltate spores with vermiculate-rugulate sculpture. Morphological distinctiveness of this new fern and its relationships with allied species are discussed and a key to these and other morphologically similar species is given.