Organophosphates (OPs) form a large group of chemicals in pesticides. Although they can be broken down in nature with time, OPs pose a severe health hazard to human due to their inhibitory effect on acetylcholinesterase, a major enzyme in nervous transmission. Therefore, detoxification of water and soil contaminated by OPs is important. One way of achieving this is by bioremediation of sites with OP-degrading enzymes. One such enzyme is methyl parathion hydrolase (MPH) isolated from Pseudomonas sp. WBC-3. Although MPH can hydrolyse a wide range of OP compounds, the substrate specificity of the enzyme is not well characterised. The substrate profile characterisation done in this work revealed that MPH is highly efficient towards methyl parathion (1 x 10⁶ M^-1s^-1), but its activity towards other OPs varies. Thus, site saturation mutagenesis (SSM) and DNA shuffling were performed to find mutants with improved activities on ethyl paraxon (6.1 x 10³ M^-1s^-1). Site saturation mutagenesis was performed on nine active site lining residues identified.  Ten single-site mutants with modest activity enhancement towards ethyl paraoxon were isolated, characterized and used as templates for DNA shuffling. Two rounds of staggered extension process (StEP) DNA shuffling were performed and 14 multiple-site mutants with further enhancement were isolated. One mutant, R2F3 exhibited 98-fold increase in k_cat/K_mvalue for ethyl paraoxon (5.9 x 10⁵ M^-1 s^-1). Several other mutants exhibited interesting but respectable changes in their substrate profiles, highlighting the ‘plasticity’ of MPH active site that allows efficient hydrolysis of other OPs with only minor changes.