OBJECTIVE To evaluate the effect of a 50% ethanolic extract of the leaf of Stephania hernandifolia and the root of Achyranthes aspera on sperm motility and function in a ratio of 1:3 by weight at different concentrations. RESULTS Concentration of 0.08 g/mL of the extract affected the motility, and at a concentration of 0.16 g/mL, the sperm motility was reduced to 20% immediately (within 20 s). At a concentration of 0.32 g/mL, this composite extract showed the most promising results by complete sperm immobilization within 2 min after the application of the extract. The effects were spermicidal but not spermiostatic as sperm immobilization effect was found to be irreversible. Sperm viability was decreased significantly and was found to be nonviable after 30 min when treated with the composite extract at a concentration of 0.32 g/mL. The hypo-osmotic swelling of these sperm was reduced significantly at this highest concentration, indicating that the crude extract may probably cause injury to the sperm plasma membrane. A low concentration of 0.04 g/mL is ineffective. CONCLUSION The findings indicate that this composite plant extract possesses potential contraceptive spermicidal activity in vitro.