Vascular invasion of gastric carcinoma were studied in 102 cases of resected stomach cancer from view of the connective tissue's proliferation. 1) Blood vessel invasion were classified in three types, as follows: Extraluminal type, Embolus type and Floating type. Extraluminal type included invasion of tumor cell out of intima. The common type of blood vessel invasion in well diff. adenocarcinoma were embolus and floating type, while in poorly diff. adenocarcinoma were extraluminal type. 2) The lymph vessel invasion were more prominent in poorly diff. adenocarcinoma. 3) From electron microscopic observation of connective tissue's proliferation, in medullary carcinoma, embolus and floating type were more frequently than extraluminal type. Conversely, in scirrhous carcinoma. Extraluminal type was the most common. These findings indicated that type of vascular invasion might be strongly affected not only by cancerous proliferation but also by connective tissue's proliferation.