Propanil， one of the most extensively used post-emergent contact herbicides， has also been reported to have adverse effect on environmental safety. A bacterial strain of Ochrobactrum sp. PP-2， which was capable of transforming propanil， was isolated from a propanil-contaminated soil collected from a chemical factory. An arylamidase gene mah responsible for transforming propanil to 3，4-dichloroaniline (3，4-DCA) was cloned from strain PP-2 by shotgun method and subsequently confirmed by function expression. The arylamidase Mah shares low amino acid sequence identity (27-50%) with other biochemically characterized amidases and shows less than 30% identities to other reported propanil hydrolytic enzymes. Mah was most active at pH 8 and 35 °C. Mah had a remarkable activity toward propanil (K = 6.3 ± 1.2 µM)， showing the highest affinity efficiency for propanil as compared with other reported propanil hydrolytic enzymes. Our study also provides a new arylamidase for the hydrolysis of propanil.