A new asplenioid fern species, Asplenium simaoense (Aspleniaceae), found growing on an exposed slope of a limestone mountain in southwestern Yunnan, China, is described and illustrated. A preliminary phylogenetic analysis showed that A. simaoense is strongly supported as sister to A. tenuifolium, whereas A. simaoense is morphologically most similar to A. varians and A. sarelii. However, A. simaoense has rhizome scales entire and petioles (5–)12–20(–25) cm, while A. varians has rhizome scales subentire or fimbriate and petioles (0.5–)2–7(–12) cm and A. sarelii has rhizome scales denticulate and petioles 7–10 cm. Only one population of A. simaoense was found near a road. Its habitat is threatened by road construction and therefore it is recommended to be classified as CR, Critically Endangered, following IUCN red list criteria.