We reported two cases of venous thrombosis occurred during systemic chemotherapy for colorectal cancer. Case 1: A 68-year-old male, who had been operated for rectal cancer received systemic chemotherapy with liver and lung metastases. Three months after the chemotherapy, the chest CT showed venous thrombosis. Case 2: A 53-year-old female, who had been operated for rectal cancer received systemic chemotherapy with lung metastases. Ten months after the chemotherapy, the contrastradiogram from catheter showed venous thrombosis. Venous thrombosis should be considered when CV ports were placed especially with systemic chemotherapy for colorectal cancer.