Objective:To determine the release and in vitro transdermal rate of tetrahydropalmatine in Xiaoji Aitong cataplasmas in rats. Methods:Using the self-made drug release determination devices and the modified Franz diffusion cells, and the skin of rats as the barrier, the release and in vitro transdermal rate of tetrahydropalmatine in Xiaoji Aitong cataplasmas were detected by HPLC. Re-sults:Tetraydropalmatine within the range of 0. 51-10. 22 μg showed a good linearity (r=0. 999 7), and the average recovery was 98. 49%(RSD=0. 84%,n =9). The release of tetrahydropalmatine in 80 min was 63. 60%, and the skin permeation rate was 23. 15% in 24h. Conclusion:Xiaoji Aitong cataplasmas have good drug release and transdermal performance.