Abstract: OBJECTIVE To establish an HPLC method for determining the content of IMC-submicron emulsion gel and study the drug permeation in vitro rat skin. METHODS The HPLC system consisted of analytical column of Hypersil BDS C18 (4.6 mm×250 mm, 5 μm), mobile phase of a mixture of acetonitrile-water-acetic acid (50∶50∶0.06), the flow rate of mobile phase was 1.0 mL·min-1. UV detector was set at 228 nm, and the coloumn temperature was 40 ℃. It was determined by externalstandard method. The drug pemeation amount in vitro rat skin was detected by modified Franz diffusion cell. RESULTS The linearity between concentration and peak area ratio was obtained from 8.46-126.90 μg·mL-1 (r=0.999 9). The mean recovery of IMC were 99.60%, RSD was 0.20% (n=9). The average pemeation amount of IMC-submicron emulsion gel in 24 h was (1311.38±74.95) μg·cm-2, permability rate was (54.17±4.91) μg·cm-2·h, and the permeation behavior in vitro followed the zero-order kinetic equation. CONCLUSION The method built in this study is accurate and reliable, applicable to assay the content and to evaluate the transdermal character in vitro of this preparation.