Introduction & Objective: Based on the other studies that had shown preoperative coagulation tests and fibrinolysis factors have correlated with different malignancies and degree of extension of these tumors, we have checked preoperative plasma levels of D-dimer, fibrinogen, PT, PTT, Hb, WBC count and the formation of platelets in the gastric cancer patients and control group to assess the relationship between preoperative plasma levels of these factors and gastric cancer and the different pathological stages of this tumor that is high prevalent in Iran. Materials & Methods: 114 patients with gastric cancer and 114 patients with benign gastric disease were assessed in our case-control study and we evaluated plasma levels of these factors in their plasma samples, 24 hours before their operations or upper GI endoscopies. The pathological stages of gastric tumors were assessed according to AJCC (American Joint Committee of Cancer) protocol and manual. Results: The plasma D-dimer level, plasma fibrinogen level, platelet count, platelet abnormal formation, Hb and PTT levels were significantly correlated with gastric adenocarcinoma. Based on the logistic regression analysis, this correlation was stronger for plasma D-dimer level, plasma fibrinogen level and abnormal platelet formation in PBS. Plasma D-dimer level was significantly correlate with resectability of tumor, distant metastasis and the clinical stages of this tumor, but there was no significant correlation between this factor and lymph node metastasis, tumor site and the type of gastric adenocarcinoma. We also found no significant correlation of PT level and WBC count with gastric cancer in this study. In this study the cut off points of plasma D-dimer level and plasma fibrinogen level were 0.15 mg/lit and 400 mg/dl respectively.The sensitivity and specificity of D-dimer in diagnosis of gastric cancer was 54% and 84%, and the sensitivity and specificity of fibrinogen was 79% and 63% respectively. Conclusions: Preoperative levels of plasma D-dimer and fibrinogen and the abnormal platelet formation in PBS can be diagnostic factors in the presence of gastric cancer. Also, preoperative plasma D-dimer level can be a predictor of the extension of this tumor.