Objective：To investigate the expression changes of SOX9 in gastric cancer tissues and its relationship with clinicopatho－logical characteristics and prognosis of patients with gastric cancer. Methods：The clinical data of 180 patients with gastric cancer treated in our hospital from June 2014 to June 2017 were collected. The expression of SOX9 protein in the patients’ gastric cancer tissues and adjacent normal tissues were detected using immunohistochemical staining. The relationship between SOX9 protein level and clinicopathological features，prognosis and prognostic factors of patients with gastric cancer was analyzed. Results：Immuno－histochemical staining showed that SOX9 protein was mainly expressed in the nucleus of gastric cancer and adjacent tissues. The ex－pression of SOX9 protein in 180 gastric cancer tissues and adjacent tissues was 154（85.56%） and 34（18.89%），respectively. The difference in SOX9 protein expression between the two groups was statistically significant（ χ2=160.317，P=0.000）. The expression of SOX9 protein was correlated with clinical stage，degree of differentia－tion，lymph node metastasis and invasion of muscular layer（ χ2=6.868，P=0.009； χ2=9.554，P=0.002； χ2=30.456，P=0.000； χ2=29.738，P=0.000）. The median progression-free survival and total survival of patients with positive SOX9 expression were significantly lower than those of patients with negative expres－sion（log-rank=3.193，P=0.015；log-rank=5.109，P=0.009）. In Cox proportional risk regression model，the expression of SOX9 pro－tein was an independent risk factor affecting the overall survival and progression-free survival（P=0.009，P=0.006）. Conclusion：The expression level of SOX9 protein is closely related to the clinicopathological characteristics and prognosis of gastric cancer patients，and can be used as an auxiliary marker in the diagnosis of gastric cancer.