Abstract: 3H tracing method is used to observe the IN's (Indomethacin, IN) biological distributions and anti-tumor effects in C57 mice with Lewis lung cancer. The results show that IN concentrats selectively in tumor tissues. At 7 h after giving IN, the radioactivity uptake in tumor tissue is higher than that in blood, muscle and fat (P<0. 05). At 12 h the radioactivity uptake in tumor is significantly higher than other tissues (except for liver and kidney) (P<0. 01). The results of IN in suppressing tumors show that the tumor volume in the treatment group is 3. 59 cm3 whereas 8. 37 cm3 in the contrast group at 20th day after tramsplamting of Lewis lung cancer. The inhibitory ratio is 57. 1%. IN is given early after the transplanting of Lewis lung tumor, no tumor is observed at the location of transplantation. It shows IN's potential role in anti-tumor effects.