Phyllanthus niruri has been found to exhibit marked inhibitory effect on hepatitis B virus evident by its exhaustive utility in cases of chronic jaundice. However, till date, research has not been focused on identification and validation of active pharmacophores of Phyllanthus niruri responsible for the reported inhibitory effect of its aqueous extract on anti-human immunodeficiency virus. The present investigation examines the anti-HIV effects of the alkaloidal extract of Phyllanthus niruri in human cell lines. The inhibitory effect on HIV replication was monitored in terms of inhibition of virus induced cytopathogenecity in MT-4 cells. The alkaloidal extract of Phyllanthus niruri showed suppressing activity on strains of HIV-1 cells cultured on MT-4 cell lines. The CC50 for the extract was found to be 279.85 microgmL(-1) whereas the EC50 was found to be 20.98 microgmL(-1). Interestingly the Selectivity Index (SI) was found to be 13.34, which showed a clear selective toxicity of the extract for the viral cells. The alkaloidal extract of Phyllanthus niruri was thus found to exhibit sensitive inhibitory response on cytopathic effects induced by both the strains of human immunodeficiency virus on human MT-4 cells in the tested concentrations.