Methanol was produced from methane with a high conversion rate using a high cell density process with Methylosinus trichosporium OB3b in the presence of a high concentration of phosphate buffer. More than 1.1g/L methanol accumulated in the reaction media under optimized reaction conditions (17g dry cell/L, 400mmol/L phosphate, and 10mmol/L MgCl<SUB>2</SUB>) in the presence of 20mmol/L sodium formate. The conversion rate of methane was over 60%. About 0.95g/L methanol was produced when the biotransformation was carried out in a membrane aerated reactor into which methane and oxygen were introduced via two separate dense silicone tubing. Our results provide an efficient method and a promising process for high-rate conversion of methane to methanol.