Dehydrins are involved in the prevention of osmotic damage in plants. Many studies have shown that overexpression of dehydrin genes can enhance the osmotic stress tolerance in transgenic plants. Our previous studies showed a YnSKn-type dehydrin gene WZY2 could be induced by polyethylene glycol (PEG), cold, indole-3-acetic acid (IAA), salicylic acid (SA) and abscisic acid (ABA). In the present study, we examined the phenotype and physiological indices in a dehydrin gene WZY2 RNA interference (RNAi) lines in wheat. Real-time PCR indicated a depressed WZY2 gene expression in transformed wheat. Furthermore, transgenic wheat showed lower relative water content, oxidative-related enzyme activities and higher malondialdehyde (MDA) content than wild-type bread wheat (Zhengyin No.1) under osmotic stress. Overexpression of the WZY2 in Arabidopsis thaliana (L.) Heynh. revealed a significant increase in tolerance to drought stress. Further studies also showed that WZY2 could participate in ABA-induced stomatal closure. These results demonstrated a key function of WZY2 in plant response to osmotic stress.