---

Background: Angiogenesis is a complex process that occurs in many physiologic and pathologic conditions such as invasion and metastasis of tumors. Therefore, it is the target of many clinical treatments. Rapamycin is one of the immune system inhibitor drugs that recently has been used for controlling different types of cancer. In this study, the effect of Rapamycin on angiogenesis in chicks' chorioalantoic membrane was investigated. Methods and Materials: In this experimental study, we used 42 Ross fertilized eggs that were divided into 3 random groups: control, sham-exposed (treated by Dimethyle sulfoxide-DMSO- ) and treated with Rapamycin. In 2th day, a window was opened on eggs in the sterile condition. Later, in 8th day, a gelatin sponge appeared on chorioalantoic membrane and was soaked with 5 μl Rapamycin in treatment group and 5 μl DMSO in the sham-exposed group. In 12th day, CAMs were examined and photographed by Research Photostereomicroscope in all cases. The numbers and lengths of vessels around the sponges were measured and compared with each other by T-Test (p<0.05). Results: The mean of number (42 ±7.26 ) and length (57.25±5.05 cm ) for vessels in the control group and mean of number (42.93±8.37 ) and length (55.66±10.44 cm) in sham-exposed group was'nt any significant differences. There was a significant decrease in mean number (29.36±5.28) and length (44.55±10.22) of vessels in Rapamycin with control group. Conclusion: It seems Rapamycin has an inhibitory effect on angiogenesis in chicks' chorioalantoic membrane. It decreases the number and length of vessels around treated area