Abstract: OBJECTIVE To explore the effects and mechanism of artemisia oil and its nanoemulsion on transdermal absorption in vitro of celastrol. METHODS Firstly, the method for determination of celastrol content was established. Then, the nanoemulsion with artemisia oil as the oil phase was prepared and characterized. Finally, transdermal tests were performed by improved Franz diffusion cells in order to investigate the effect of different concentrations of artemisia oil and its nanoemulsion on the transdermal penetration of celastrol. HE staining and differential scanning calorimetry were applied to evaluate the skin stratum corneum changes. RESULTS The method for determination of celastrol content had a good linear relationship in the detection range of 1.8-360 μg·mL^-1, and the linear regression equation was Y=16 494X-16 111(r=1.000). The RSDs of precision and stability were <2%. The average recovery of celastrol was 99.26%, RSD was 1.04%. The average diameter of celastrol nanoemulsion was (19.93±0.19)nm, Zeta potential was (17.67±2.78)mV and the polydispersity index was 0.097. Nanoemulsion(not containing artemisia oil), artemisia oil and its microemulsion could enhance the transdermal permeability of celastrol and change the skin structure and temperature to different degrees, but the effects varied. Among them, microemulsion containing artemisia oil was the optimum option to improve the percutaneous absorption of celastrol at a highest level. CONCLUSION Artemisia oil has a good penetration-promoting effect on celastrol, and its penetration-promoting mechanism is related to affecting the structure of the skin and changing the thermodynamic properties.