Abstract: ObjectiveTo explore the role of PDCD5 protein in diagnosis and prognosis of gastric cancer through the analysis of the relationships between PDCD5 protein and biological behavior of cancer. MethodsImmunohistochemical staining (SP method) for PDCD5 was performed in 50 cancer tissues and 50 adjacent tissues samples, the expression level of PDCD5 protein was analysed by microscope ratings and Image-Pro Plus 6.0 software. ResultsThe positive rate of PDCD5 protein in gastric cancer tissues (22.0%) was significantly lower than that in adjacent tissues (76.0%). The positive expression rate in cancer tissue was related to degree of tumor differentiation (P<0.01), depth of tumor invasion(P<0.05) and lymphatic metastasis (P<0. 05). Semiquantitative analysis showed that the value of IOD in gastric cancer tissues(8033.83±7719.14) is significantly lower than that in adjacent tissues (50224.35±39934.31).And there was a significant correlation between the IOD level and the degree of differentiation, infiltrating and lymph metastasis (P<0.01). ConclusionThe results of microscope ratings were consistent with image analysis software. The marked difference of PDCD5 protein expression between gastric cancer and normal samples was observed. Lower expression of PDCD5 indicated stronger invasive tumors and PDCD5 protein might be a biomarker for prognosis of gastric cancer.