A pendimethalin nitroreductase was purified from Bacillus circulans to 52 fold increase with a recovery of 21.1% and had a specific activity of 4.16 U/mg. The molecular weight was 27 kDa. The optimum pH and temperature were 7.5 and 35°C, respectively. Fe 2+ , Ca 2+ , Mg 2+ and Mn 2+ did not cause any effect on the enzyme activity, whereas Ag + , Hg 2+ significantly inhibited it. The pendimethalin nitroreductase from B. circulans required NADPH as cofactor. It was not affected by GSH, DTT, L Cys and β mercaptoethanol but inhibited by p hydroxymercuribenzoate, N ethylmaleimide, and iodoacetamide. EDTA, 1,10 phenan throline and α,α' dipyridyl had a moderate effect on the enzyme activity. The nitroreductase reduced all the tested nitroaromatic compounds but was more active towards pendimethalin and trifluralin. The K M and V max for the enzyme reaction using pendimethalin as a substrate were 4.35 μM and 620 μmoles mg -1 min -1 , respectively. The broad substrate specificity towards dinitroaniline herbicides suggested the enzyme to be used as a potent reducing agent of these toxic compounds. This is the first report for the purification and charac terization of pendimethalin nitroreductase from any bacterial or fungal species.