As the currently available therapies for HIV-1 have high costs and are associated with the appearance of multi-drug resistant HIV-1 strains, the Indian traditional medicine system Ayurveda may provide useful alternatives. In this study, we screened the inhibitory activities of various extracts of five Indian plants for inhibitory effects on HIV-1 reverse transcriptase (RT). Water extracts of the leaves of Argemone mexicana strongly inhibited the DNA polymerase activity of HIV-1 RT, which indicated that they contained substances with inhibitor activity. Neither heat treatment at 100ºC nor proteinase K treatment of the extracts abolished the inhibitory activity, suggesting that the inhibitory substance was an organic compound rather than a protein.