Abstract: Objective 　To investigate whether urinary t ryp sin inhibitor inhibit s tumor invasion and metastasis of lewis lung carcinoma mice . Methods 　Subcutaneous ( s. c. ) implantation of 3LL cells (5. 0 ×10⁶ ) in the right subcutaneous armpit of C57BL/ 6 male mice. There were forty mice divided into five groups with random. There were physiological saline group, cyclophosphamide group, U TI2. 5 ×10⁴ u 7d group, U TI 5. 0 ×10⁴ u 7d group, U TI 10. 0 ×10⁴ u 7d group. They all started to inject at sixth day by abdominal cavity . The volume of tumors were measured at the 8th day, 10 th day, 12th day . The weight of primary tumor and lung metastasis were established by the 14 th day af ter tumor cell inoculation . Flow Cytometry was used to analyze apoptosis rate and s-phase f raction. Results 　The average weight of tumor in turn were (7. 92 ±2. 52 、0. 66 ±0. 50 ^＊＊、3. 47 ±1. 45^＊3 、3. 08 ±0. 81^＊＊3 3 、1. 70 ±1. 05^＊＊ ) g, the average number of lung metastasis were (8. 625 ±1. 407 、1. 125 ±1. 126^＊＊ 、1. 625 ±1. 302^＊＊ 、1. 00 ±0. 75^＊＊ 、0. 625 ±0. 74^＊＊) . The apoptosis rates of CTX (39. 3 ±4. 8) %^＊and U TI 10. 0 ×104 u ( 40. 2 ±3. 1) %^＊ weremarkedly increased. The s2phase f ractions of U TI cannot reduce s-phase f raction. The tumor growthcurve showed in FIG. 3. Conclusion 　Ulinastatin can inhibit primary tumors and lung metastasis carcinoma of Lewis mice.