OBJECTIVE To compare the accuracy of CT and MR including diffusion-weighted imaging(DWI) in preoperative diagnosis and T staging of gastric cancer. METHODS Forty-one patients with gastric cancers proved by gastroscopy biopsy from November 2011 to August 2012 were prospectively enrolled. They underwent contrast enhanced CT and MR imaging (including DWI, T2 weighted and dynamic enhanced imaging) preoperatively. Two radiologists interpreted CT and MR images for detecting and staging each patient independently. With the reference of post-operative histopathological findings, T staging accuracy of CT and MR imaging was calculated and compared. Inter-observer agreement was also evaluated. RESULTS Overall T staging accuracy in MR including DWI was significantly higher than that in CT imaging(87.8% vs. 65.9%, P=0.004). MR had a better inter-observer agreement than CT(Kappa=0.813, 0.603, respectively). CONCLUSIONS MR including DWI can improve preoperative T staging accuracy of gastric cancer significantly, which deserves recommendation for clinical application.