Abstract: The aim of this study was to evaluate the potential of Argemone mexicana (Shialkanta) extract as antimicrobial agent against bacterial isolates originated from drinking water. Effectiveness of acetone extract, ethyl acetate extract and petroleum ether extract of Argemone mexicana was determined in vitro, using agar diffusion method and MIC determination test against four (one Gram positive and three Gram negative) water borne pathogenic bacteria Escherichia coli, Shigella sp. Staphylococcus sp. and Salmonella sp. The zones of inhibition against the tested bacteria were found ranging from 8 to 16 mm, along with their respective MIC values ranging from crude to 512 μg mL-1. This study suggests that natural products derived from Argemone mexicana may contribute to the development of new antimicrobial agents.