Abstract: OBJECTIVE To prepare a eugenol microemulsion gel with high drug content and adhesiveness, so as to improve transdermal penetration and relative bioavailability of eugenol. METHODS The solubilities of eugenol in oils, surfactants and cosurfactants were evaluated by apparent solubility to screen the components of microemulsion. Pseudo-ternary phase diagrams were constructed by using ethyl oleate, Solutol HS15, PEG 400 and purified water as the oil phase, surfactant, cosurfactant and water phase, respectively. The pH, conductance, viscosity, particle size and drug concentration of this microemulsion were measured. The optimized system was formulated into a gel form by using Carbopol 940 and glycerin, and its pH, particle size, viscosity, drug concentration were evaluated. And its in vitro diffusion performance were evaluated by improved Franz diffusion cell method. RESULTS When the surfactant/cosurfactant ratio was 1:1, the largest microemulsion region formed. The particle size of microemulsion F3 was 83.27 nm, with a stable content. A homogeneous and transparent microemulsion gel was obtained by adding 0.5% carbopol 940 and 6% glycerin. The viscosities of microemulsion F3 and microemulsion gel FG3 were 106.8 mPa·s and 15.7 Pa·s respectively. Percutaneous penetration studies using rats' skin in vitro showed that the cumulative infiltration rates of eugenol standard solution, microemulsion and microemulsion gel followed an ascending order. The 12 h cumulative infiltration amount of eugenol microemulsion gel FG3 reached 55.08%. Rabbit irritation study exhibited that the skin was not irritated or inflamed. CONCLUSION Eugenol microemulsion gel has higher applicability and stability than those of eugenol standard solution and eugenol microemulsion, it is promising as a new drug delivery formulation.