Methylosinus trichosporium OB3b was cultured in the bioreactor to enhance cell growth rate by increasing mass transfer rate of methane into NMS medium. Mixture gas with methane and oxygen were introduced into the bioreactor. First, mass transfer coefficient (kLa) was determined, and then cells were cultivated. Methane was converted to methanol by adding chemical inhibitors of methanol dehydrogenase under the optimized condition. Conversion of methane to methanol was enhanced by improving the mass transfer rate to keep high methane concentration in the medium.