The synthesis of dimethoxydiphenylmethane (DMODPM) from the reaction of methanol and dichlorodiphenylmethane (DCDPM) was successfully carried out in a liquid-liquid phase-transfer catalytic (LLPTC) reaction assisted by ultrasonic irradiation. Little of the desired product DMODPM was obtained from the reaction in the presence of only potassium hydroxide and quaternary ammonium salts. The production of the DMODPM product was greatly enhanced when the reaction system was irradiated by ultrasonic waves. Two sequential reactions in the organic-phase solution proceed to produce the desired product. However, the second rate of the organic-phase reaction was faster than the first. Therefore, the first intermediate product, chloromethoxy-diphenylmethane (CMODPM), was not detected during or after the reaction. A kinetic model was developed based on the experimental data. A pseudo-steady-state hypothesis (PSSH) was employed to describe the characteristic behaviors of the kinetic data. The results were finally described by a pseudo-first-order rate law, from which the apparent rate constant (k(app,l)) of the first organic-phase reaction was obtained. The effects of the reaction conditions on the conversion of DCDPM and the reaction rate were investigated in detail, including the agitation speed; the amounts of methanol, DCDPM, water, chlorobenzene, potassium hydroxide, and tetrabutylammonium bromide (TBAB); the ultrasonic power and frequency; the organic solvents; the quaternary ammonium salts; and the temperature. Rational explanations are provided for the experimental results.