A new species, Castanopsis glabrifolia J. Q. Li & Li Chen, and one new name, C. hsiensiui (X. M. Chen & B. P. Yu) J. Q. Li & Li Chen (Fagaceae), are described from Hainan, China. They both grow on sandy beaches. Castanopsis glabrifolia is closely related to C. chinensis (Spreng.) Hance, differing from it by having smaller leaves, shorter petioles, fewer secondary veins, and smaller cupules that are incompletely covered by shorter spines. Castanopsis chinensis var. hainanica X. M. Chen & B. P. Yu is treated as a new synonym of C. glabrifolia. The new name C. hsiensiui is proposed, based on C. hainanensis Merr. var. litoralis X. M. Chen & B. P. Yu, with the variety recognized at higher rank based on its glabrous branches and petioles, the smaller cupules with the external surfaces visible, and the nuts that are glabrous or sparsely pubescent near the apex.