Organophosphorus (OP) degrading enzymes were widely used in economical and safe detoxification of organophosphorus pesticides from soil, water, food, and aquatic product. In this study, a novel methylparathion degrading enzyme (MPD) was over-expressed in Escherichia coli BL21 (DE3) as a His-tagged fusion protein by the use of lactose as inducer instead of IPTG. SDS-PAGE combined with enzyme activity analysis indicated that lactose-induced expression yield of active MPD was increased nearly 2-fold compared with IPTG as inducer. The optimum temperature and concentration for lactose induction was 37 °C and 0.5 % (w/v), respectively. The expressed fusion proteins induced by the two inducers were both purified by Ni-metal-affinity chromatography. The specific activity of the purified recombinant MPD induced by lactose, reaching at 140 mol•min-1•mg-1, was nearly 0.5-fold higher than that of the purified enzyme induced by IPTG. Thus, lactose was a well alternative inducer to produce active MPD and gave an advantage over enzyme purification. This study suggested a more effective method to produce purified MPD, an ideal enzyme to detoxify OP pesticides for ecosystem restoration.