OBJECTIVE To research the trichomonacidal effect of secnidazole benzoate in vitro. METHODS Trichomonas vaginalis was cultured in liver extract medium in 96-well microplate. The culture suspension of Trichomonas vaginalis was divided into four groups: secnidazole benzoate, secnidazole, metronidazole and control, with medium as blank control. MTT colorimetric assay was applied to determine the inhibitory effect of secnidazole benzoate on the proliferation of Trichomonas vaginalis. The culture suspension was transferred into test tubes and divided into same groups to observe inhibitory effect by the classical microscopic counting method. RESULTS After 24 h incubation, the proliferation of the parasites was concentration-dependent by secnidazole benzoate (t = 9.02, P < 0.01) at the concentration ranges from 0.15 microg/ml to 20.0 microg/ml with a relative inhibition rate (%) of 14.6, 28.7, 31.3, 60.4, 89.0, 89.2, 95.6, and 100.0 for MTT colorimetric assay, and 18.2, 31.1, 39.7, 68.8, 84.6, 90.1, 94.6, and 100.0 for counting method, respectively. In the period of 6-24 h incubation, the inhibition was in a time-dependent manner. The minimum sterilizing concentration and the minimum inhibitory concentration were 20 microg/ml and 0.15 microg/ml respectively. CONCLUSIONS Secnidazole benzoate shows a similar trichomonacidal effect to metronidazole and secnidazole.