T WO BACTERIAL strains were isolated by soil enrichment technique and identified as Lysinibacillus sphaericus DM-3 and Bacillus cereus DM-5. Biodegradation experiments were performed in carbon free-mineral salt media supplemented with 100 mg/L of dimethoate. The ability of bacterial strains to degrade the dimethoate was evaluated under various conditions such as pH range, temperature and different concentrations of dimethoate. The dimethoate residue was determined quantitatively by HPLC method and the degradation byproducts were identified by GC/MS technique. The results revealed that both bacterial strains can utilize dimethoate as a sole carbon source up to a concentration of 500 mg/L. The optimum temperature for both strains to degrade dimethoate was 28°C. L. sphaericus DM-3 and B. cereus DM-5 showed maximum growth in the presence of dimethoate at pH 6.0 and 7.0, respectively. L. sphaericus DM-3 could degrade 24% of dimethoate within 72 h, whereas the degradation percentage using B. cereus DM-5 was 17% after the same incubation period. The main byproducts from the degradation of dimethoate by L. sphaericus DM-3 and B. cereus DM-5 was namely O,O,S-trimethyl phosphorothioate. This study reports for the first time the efficient ability of L. sphaericus DM-3 and B. cereus DM-5 to degrade dimethoate, up to 500 mg/L, over a wide range of pH.