The objective of our study is to investigate the in vitro antibacterial activity of ethanolic leaf extract of Aerva lanata and root extract of Hemidesmus indicus against acidogenic oral microbe Streptococcus mutans .The inhibitory effect of the extract were tested against S.mutans by using the Macro broth dilution method .The ethanolic leaf extract of Aerva lanata exhibited antibacterial activity against streptococcus mutans with minimum bactericidal concentration of 400mg/ml whereas the MBC for Hemidesmus indicus did not showed any activity even in higher concentrations. The ethanolic leaf extract of Aerva lanata was found to be bactericidal in action against tested bacterial strain and these actions may be due to the presence of phytochemical constituents in it.