Objective:To investigate the correlation between the expressions of miR-524-5p and sex determining region Y box protein 9 (SOX9) in advanced gastric cancer and their influences on the efficacy and prognosis of chemotherapy.Methods:A total of 82 patients diagnosed as advanced gastric cancer who received DCF (docetaxel + cisplatin + fluorouracil) chemotherapy in 910th Hospital of Joint Logistics Support Force of Chinese People′s Liberation Army from January 2015 to December 2017 were selected as the research objects. The expression levels of miR-524-5p and SOX9 in gastric cancer tissues were detected by fluorescence quantitative PCR. The correlation between the expressions of miR-524-5p and SOX9 was analyzed, the total effective rates of chemotherapy in patients with different miR-524-5p and SOX9 expression levels were compared, and the predictive value of miR-524-5p combined with SOX9 on the efficacy of chemotherapy was analyzed. Overall survival (OS) and progression-free survival (PFS) were analyzed.Results:The expressions of miR-524-5p and SOX9 were not related to gender or age of patients with advanced gastric cancer (all P>0.05), but were related to the degree of differentiation ( χ2=3.577, P=0.001; χ2=5.654, P<0.001) and distant metastasis ( χ2=2.466, P=0.016; χ2=5.218, P<0.001) of patients with advanced gastric cancer. There was a negative correlation between the expressions of miR-524-5p and SOX9 in advanced gastric cancer ( r=-0.348, P=0.001). According to the median expressions of miR-524-5p and SOX9 in gastric cancer tissues, patients were divided into high expression and low expression groups, miR-524-5p≥0.64 was high expression ( n=41), <0.64 was low expression ( n=41), SOX9≥1.84 was high expression ( n=41), and <1.84 was low expression ( n=41). The total effective rate of advanced gastric cancer patients with high expression of miR-524-5p was 58.54% (24/41), which was higher than that of patients with low expression of miR-524-5p (24.39%, 10/41), and there was a statistically significant difference ( χ2=9.484, P=0.002). The total effective rate of advanced gastric cancer patients with high expression of SOX9 was 21.95% (9/41), which was lower than 60.97% (25/41) of patients with low expression of SOX9, and there was a statistically significant difference ( χ2=12.863, P<0.001). Receiver operating characteristic curve analysis showed that the expressions of miR-524-5p and SOX9 had predictive value for the efficacy of chemotherapy, and the area under the curve was 0.753 (95% CI: 0.644-0.861, P<0.001) and 0.660 (95% CI: 0.540-0.780, P=0.014) respectively. The combination of miR-524-5p and SOX9 had predictive value for the efficacy of chemotherapy, and the area under the curve was 0.768 (95% CI: 0.667-0.868, P<0.001). The median PFS and OS of patients with high expression of miR-524-5p were 8 months and 14 months, which were longer than those of patients with low expression of miR-524-5p (6 months, 9 months), and there were statistically significant differences ( χ2=21.160, P<0.001; χ2=29.730, P<0.001). The median PFS and OS of patients with high expression of SOX9 were 7 months and 10 months, which were shorter than those of patients with low expression of SOX9 (8 months, 12 months), and there were statistically significant differences ( χ2=6.345, P=0.012; χ2=4.107, P=0.043). Conclusion:There is a negative correlation between the expressions of miR-524-5p and SOX9 in advanced gastric cancer tissues. The chemotherapy efficacy and prognosis of patients with high expression of miR-524-5p and low expression of SOX9 are better than those of patients with low expression of miR-524-5p and high expression of SOX9.