Patients with rectal cancer of stage dukes B and C were randomized into two groups. In osmosis chemotherapy group 86 patients were treated by radical resection plus adjuvent preoperative intraluminal 5-FU osmosis chemotherapy at the area of tumor. In control group 74 patients were treated by radical resection alone. There were high concentration of 5-FU in the cancer, mucosa and lymph node around the cancer and mesenterica inferior venae, and the lower in a round venae. After the chemotherapy the symptoms were improved without side-effects, the II-III grade at pathological change was 83%, the cancer regression more than 50 was 38%. Compared the two groups osmosis chemotherapy raised 14% at radical resection and reduced 22%, 11%, 22% at local recurrence and metastasis of lymph nodes and liver. The 3-, 5-year survival rates (81.1%, 69.6%) were higher than 19.2%, 26.7% in the control group.