The purpose of this study was to investigate the effect of Tween 80 on the diaphaneity of a kind of film-forming tolterodine hydrogel, and find optimum content of Tween 80 applied to improve the appearance.Preparation of the hydrogels consisted of three steps.Firstly, Carbomer 980, hydroxypropyl cellulose (HPC) and hydroxypropyl methyl cellulose (HPMC) were mixed quantitatively and then swelled for 12 h in a beaker holding 6 ml deionized water at room temperature.Secondly, tolterodine tartrate was converted to tolterodine free base by NaOH saturating ethyl alcohol solution.Finally, drug was loaded to the matrices and weight of the system was adjusted to 10 g by deionized water.Different content of Tween 80 (0%, 1%, 2%, 3%, 4%, 5%, 6%, 7% and 8%, w/w) were added to the matrices in the first step for studying the effect of Tween 80 on the diaphaneity of the hydrogels.Real-time morphology observation was carried out at 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 5 min, 10 min, 20 min and 30 min after the hydrogels were smeared on microslides.Two of the results were showed in Figl and Fig2, it was found that the hydrogels were transparent at the beginning, then tolterodine separated out and the hydrogels turned white quickly within 3 min.The hydrogels of groups in which content of Tween 80 was 0-4% remained white with continuous observation within 30min, however, the hydrogels turned transparent gradually and thoroughly when content of Tween 80 was more than 5%, but high content of Tween 80 which was above 7% would be a bad fator for forming film.It could be explained that at the beginning the volatilization of ethyl alcohol resulted in high water content and caused tolterodine to separate out.Due to water evaporation and solubilization effect of Tween 80 of which content was above 5%, the hydrogels revived transparent within 30 min.From the results above we could draw a conclusion that Tween 80 was a good solubilizer for tolterodine free base to improve the diaphaneity of a kind of film-forming tolterodine hydrogel, besides, there was an optimum content which was 5%-7%.