Abstarct: Human activities and industrialization have increased the concentration of harmful elements such as heavy mextals in the ecosystem and have devastating effects on the food health of organisms. Lead (Pb(II)) is one of the heavy mextal elements causing harmful effects on ecosystems and living organisms. Bacteria, as the divers organisms, are used as part of microorganisms involved in the process of Pb(II) bioremediation. In the present study, the effects of long-term Pb(II) contamination (LTC) under a continuous sub-culturing system were evaluated on the growth rate, Pb-remediation potential, Pb-remediation mechanisms, morphological and genetically modifications of two strains, CM3 and CM7, of Microbacterium oxydans. Our findings illustrated that LTC could affect the optimal pH and temperature, and LTC was able to increase the growth rate of bacterial strains in the Pb(II) environment comparing with native strains. Besides, the Pb-remediation potential of strains from LTC was sharply increased at pH 6.5. The biomass of strains was analyzed in terms of the topographical and elements percentage using SEM. Our observations resulted that LTC could not change the cell shape and cell dimensions of studied strains. Besides, we found a correlation between P and Pb(II) percentage in biomass of strains from LTC, indicating these strains more precipitated Pb(II) in forms such as lead sulfate, and lead phosphate to reduce toxicity. Furthermore, LTC had reduced the Pb(II) accumulation into the cell wall of strains. In addition, the Pbr operon was not detected in the genome of studied strains indicating that they used other lead transporters to exit lead from cytoplasm.