Four mutants (DLL-E1, DLL-E2, DLL-E3 and DLL-E4) were obtained by UV and LiCl mutation breeding of Methyl Parathion degrading strain Pseudomonas sp. DLL-1. Studies on their abilities to degrade Methyl Parathion and p-nitrophenol, substrates, activities of ectoenzyme and crude enzyme showed that all mutants have higher biological activities compared to the original strain. Further studies on resistance and degradation of Methyl Parathion and p-nitrophenol by DLL-E4 was conducted.