Abstract-Semiconductive nanoparticles of bacteria as Bacillus subtilis with catalyst MgFe2O4 biofilm was synthesized by using solution combustion technique. The process was convenient, environment friendly and efficient method. Materials were characterized by TG/DTA, XRD, and TEM. Thick biofilm of Bacillus subtilis MgFe2O4 was measured by exposing it to reducing economical gases. It was found that the Bacillus subtilis was sensors exhibited various sensing responses to these gases at different operating temperature. The sensor exhibited a fast response and a good recovery. The biofilm can be used as a new type of gas-sensing material which has a high sensitivity and good selectivity to various gases at low ppm.