Bioremediation is the removal of heavy-metals such as nickel (Ni) using microorganisms and has been considered as an important field in the biotechnology. Isolation and characterization of microorganisms exhibiting bioremediation activities and their optimization to treat polluted wastewaters is a vital and difficult task in remediation technologies. In this study, investigation was carried out to isolate Ni (II) remediating microbial strains from soils contaminated with municipal solid waste leachate. Furthermore, Taguchi design of experiments were used to evaluate the influence of concentration, pH, temperature, and time on bioremediation of Ni (II) using isolated bacteria. This study concluded that Bacillus sp. KL1 is a Ni (II)-resistant strain and had Ni (II) bioremediation activity. The highest bioremediation of Ni (II) was observed as 55.06% after 24 h at 30ºC, pH 7, and 100 ppm concentration. Moreover, it was also observed that concentration is the most effective factor in the bioremediation process. In conclusion, we have demonstrated that bacteria isolated from soils contaminated with garbage leachate have the Bacillus sp. KL1 bacteria which can efficiently uptake and eliminate Ni (II) from contaminated sites and thus makes it possible to treat heavy-metal containing wastewaters in industry by using this microorganism at optimized conditions.