Abstract: The kinetics of oxidation of methanol to formaldehyde over Pb_0.88Bi_0.06La_0.02Mo/SiO₂catalyst was described by Redox mechanism of two stages.When the particles of catalyst increased to 3 mm in diameter, the effect of intraparticle diffusion strongly depended on the rate of oxidation of methanol to formaldehyde. The effectiveness factor of catalyst was determined by experiments to be 0.38-0.73.The kinetic equation of Redox mechanism in the presence of intraparticle diffusion of oxygen was interpretated by the theory of intraparticle diffusion and proved by experiments.The apparent activation energies of oxidation of methanol in the presence of intraparticle diffusion of oxygen were determined and interpreted by the kinetic experiments and a theoritical equation.