Didymodon zanderi sp. n. (Pottiaceae, Musci) is described from Zabaikalsky Territory (former Agin-Byurayt Autonomous District) of Asian Russia. It is related to D. hedysaryformis Otnyukova, a species recently described from Tyva Republic, but differs in leaf apices only occasionally fragile, not differentiated into propagulae of definite shape, and in larger laminal cells, bulging and papillose. Didymodon zanderi is rather common in Alkhanai National Park, where it grows in abundance on rocks along mountain creeks at ca. 1000-1200 m elev., and also is known from scattered localities in mountain areas of Altai, southern Taimyr, central Yakutia, Buryatia, Primorsky Territory and Kamchatka, from 500 to 2800 m elev.