Background Insulin-like growth factor-Ⅱ mRNA-binding protein 3 (IMP3) is a newly identified mRNA-binding protein that is involved in embryogenesis and carcinogenesis of some malignant tumors. The aim of this study was to detect the expression of IMP3 protein in gastric adenocarcinoma (GAC) and the correlation with clinicopathological features.Methods IMP3 protein in 92 samples of GAC was evaluated by immunohistochemical method. The Mann-Whitney U test and Kruskal-Wallis H test were used to compare IMP3 expression and clinicopathological parameters. Kaplan-Meier survival curve, log-rank test and Cox-regression model were used to evaluate the correlation of IMP3 protein expression to the prognosis of patients.Results Out of 92 cases of adjacent normal mucosa (ANM), 10 with dysplasia demonstrated weak expression of IMP3 and 82 without dysplasia showed negative expression. Out of 92 cases of GAC, positive immunohistochemical stain for IMP3 was identified in 75 (82%) cases. A comparison of IMP3 expression in GAC and ANM showed stronger immunohistochemical reactivity in GAC (P ＜0.05). High expression of IMP3 was found to be associated with lymphoid metastasis, high Ki-67 labelling index, and patient poor outcome (P ＜0.05). There was a significant TNM stage difference between GAC with and without IMP3 expression (P＜0.05). Tumors with higher stage showed higher level of IMP3 expression, In multivariate analysis, IMP3 emerged as an independent predictor of survival.Conclusions Increase of IMP3 expression suggests that IMP3 may play an importent role in the carcinogenesis and tumor metastasis in GAC. It could be regarded as a novel proliferation and prognostic indicator for patients with GAC.