Sinojohnstonia Hu (Boraginaceae, Trigonotideae) is endemic to China and previously included only three species. Sinojohnstonia ruhuaii W. B. Liao & Lei Wang, a new species from Jiangxi, China, is described and illustrated. The new species is most closely related to S. chekiangensis (Migo) W. T. Wang by its morphology and differs in that its flowers are smaller, the corolla limb is slightly shorter than or nearly as long as the tube, and the stamens are positioned below the throat appendages. A key is provided to distinguish the four species of Sinojohnstonia now recognized.