Systemic activation of hemostasis and thrombosis has been implicated in tumor progression and metastasis. D-dimer has been used as an indicator for the thrombosis. Here, we investigated the role of the activation of coagulation in patients with metastatic gastric cancer by measuring D-dimer level.We conducted an observation study of 46 metastatic gastric cancer patients who received palliative chemotherapy (CTx). D-dimer levels were assessed before CTx and at the first response evaluation after CTx.The overall survival (OS) of patients with pretreatment D-dimer levels <1.5 μg/mL was significantly longer than that of patients with D-dimer levels ≥1.5 μg/mL (22.0 vs 7.9 months, P = 0.019). At the first response evaluation, the mean level of D-dimer was significantly decreased by 2.11 μg/mL in patients either with partial response or stable disease (P = 0.011) whereas the mean level of D-dimer, although the difference did not reach statistical significance, was increased by 2.46 μg/mL in patients with progressive disease. In addition, the OS of patients with D-dimer levels <1.0 μg/mL at the first response evaluation was significantly longer than that of patients with D-dimer levels ≥1.0 μg/mL (22.0 vs 7.0 months, P = 0.009). The lower D-dimer levels (<1.0 μg/mL) at the first response evaluation after CTx was independent predictive factor for better survival in multivariate analysis (P = 0.037).This study suggests that D-dimer levels may serve as a biomarker for response to CTx and OS in patients with metastatic gastric cancer.