A new moss species of the family Mielichhoferiaceae, Synthetodontium kunlunense J. C. Zhao & Y. Y. Liu, is described and illustrated. It was collected from soil substrates in an oasis in the Kunlun Mountains in Xinjiang Uyghur Autonomous Region in China. The peristome structure of this species is similar to that of S. pringlei Cardot, but S. kunlunense has longer leaves (0.5–1.3 mm vs. ca. 0.5 mm), shorter median leaf cells (8.6–21.7 μm vs. 40.6–72.6 μm), decurrent leaf bases (vs. not decurrent), a nodding capsule (vs. erect), and reddish proximal leaf cells (vs. green). Synthetodontium Cardot seems to be a disjunct genus distributed between East Asia and North America because the new species is known from a single locality in China, and another closely related species in the genus is known from four localities in Mexico.