Diplolepis rosae (L.), originating from North America, is recorded for the first time in China. This pest infested Rosa serrata ×R. rugosa, causing heavy economic losses in Gansu Province. In this paper, the morphologies of the larvae, adult and gall of Diplolepis rosae (L.) are described, and a key to related species is provided. At the time of discovery and identification of D. rosae, one of its natural enemies, Torymus bedeguaris (L.), was also discovered, and the parasitism ratio surveyed. The results indicate that this parasitic wasp can effectively control the population growth of D.rosae.