An organophosphorus-degrading bacterium MEW06, which exhibited excellent biodegradation capabilities towards 50 mg/L of methyl parathion (MP), paraoxon and dimethoate, was isolated from Sand Lake (Wuhan, China) and identified as Serratia marcescens subsp. marcescens based on physiological-biochemical characteristics and a 16S rDNA sequence-based phylogenetic tree. MEW06 genome contains a 31.09-kDa methyl parathion hydrolase (MPH) (MPHGM004539) that was 54.9% similar to Pseudomonas sp. WBC-3's MPH. RT-qPCR revealed that mphGM004539 gene expression was significant up-regulated when co-cultured with MP. mphGM004539 without signal peptide (mphGM004539Δsp) was successful cloned and expressed in Escherichia coli BL21 (DE3). Optimized specific enzyme activity of MPHGM004539ΔSP was 5.26 U/mg under 35°C and pH 11.0 conditions when MP as the substrate. Additionally, Co2+, Cd2+and Fe2+ increased the enzyme activity level. MP could be degraded by MPHGM004539ΔSP into p-nitrophenol probably by hydrolyzing the P-O ester bond. Virulence of MP towards Drosophila melanogaster W1118 was reduced by MEW06 or MPHGM004539ΔSP biodegradation. This is the first cloning and characterization of MPH from the organophosphorus-degrading bacterium S. marcescens. MEW06 and its MPH have potential roles in the bioremediation of organophosphorus pesticide-contaminated eco-systems.