The purpose of this study was to prepare tetramethylpyrazine hydrochloride transdermal gel and to study its permeation ability in vitro. The skin permeation ability was evaluated by Valian-Chien permeation cells with isolated rat skin. The concentration of tetramethylpyrazine in samples was determined by HPLC. The optimal formulation was composed with 5% azone, 5% peppermint oil, 8% sodium carboxymethylcellulose and 8% tetramethylpyrazine hydrochloride. The accumulative permeation amount of the gel was (6 731.87 +/- 102.31) microg x cm(-2) in 12 h,and the permeation rate was (535.02 +/- 33.89) microg x cm(-2) x h(-1). The release profile in vitro was in line with zero-order formulation. Tetramethylpyrazine hydrochloride gel prepared in the study would be developed as a novel transdermal preparation.