Lysimachia sinopilosa C.M. Hu & G. Hao sp. nova (Primulaceae) is described from Yunnan, China, and illustrated. In general morphology it resembles the species in Lysimachia subgen. Idiophyton, which are characterized by a yellow corolla, and an anther longer than filament, basifixed and opening by an apical pore. Lysimachia sinopilosa is most similar to L. pilosa, but can be distinguished by its purple indumentum on stems, petioles, peduncles and adaxial surface of leaves, by its leaf blades with a sub-rounded or obtuse base, and by its smaller flowers.