Stellaria motuoensis sp. nov. (Caryophyllaceae) is described and illustrated as a new species from Xizang of China on the basis of both morphological and molecular evidence. Phylogenetic analysis based on ITS sequence data show that S. motuoensis is closely related to S. monosperma. Morphological observation has shown that S. motuoensis is most similar to S. monosperma var. paniculata, but readily differs by its bisexual flower with no petals (versus bisexual or unisexual with petals 5), five stamens (versus 5 or 10), filiform roots (versus fusiform, thick, fleshy), terete stem (versus quadrangular), stems glabrous basally, pubescent apically (versus glandular pubescent, with 1 or 2 rows of hairs above), leaves glabrous (versus pubescent).