Serum thymidine kinase 1 (STK1) is a reliable proliferation marker in most of solid tumors, including gastric cancer.The aim of this study was to evaluate whether the STK1 levels were related to tumor response to chemotherapy and survival in advanced gastric cancer.The Results showed that the average STK1 level in patients with gastric cancer was (5.57 ± 3.07), which was significantly higher than that in the healthy controls(1.12 ± 0.57) (P < 0.001).And among all 84 patients, the average STK1 level (6.02 ± 3.12) in 56 patients without accepting surgery was higher than that (4.68 ± 2.78) in 28 patients who had accepted surgery(P =0.049).The STK1 value correlated with the clinical stage, ECOG PS and serum CEA levels(P < 0.001, P =0.001 and P =0.004, respectively), but not with age and sex.The average STK1 levels after 1, 2 and 4 cycles of chemotherapy did not significantly decrease in all patients, when compared with those levels before chemotherapy.But after 2 cycles of chemotherapy, the average level of STK1 was significantly decreased in patients who achieved objective response (OR) (CR, PR or no recurrence).Especially after 1 cycle chemotherapy, the average level of STK1 in patients who achieved OR had begun to decline, while in most of patients with disease progression or recurrence, STK1 begun to increase.Especially in patients receiving palliative chemotherapy or receiving adjuvant chemotherapy, there was a significant difference of median PFS (median PFS, no defined versus 4 months, P < 0.001) or RFS (median RFS, no defined versus 5 months, P < 0.001) between patients with STK1 decline and patients with STK1 increase during the first 2 months of chemotherapy.The log rank test shows patients with STK1 decline have a trend of longer OS in palliative chemotherapy group.Our results suggested that serum TK1 levels correlated with the clinical stage, ECOG PS and serum CEA levels in patients with gastric cancer, and the changes of STK1 levels during the first 2 months of chemotherapy may be more important for evaluating chemotherapy response, predicting PFS and RFS than the baseline values of STK1 in patients with advanced gastric cancer.