The kinetic study of the Wittig reaction of synthesizing stilbene is carried out by reacting benzaldehyde (C6H5CHO) with benzyltriphenylphosphonium chloride (BTPPC) in the NaOH (aq)/-CH2C12two-phase system, the rate of reaction depends on the agitating speed, temperature, and the concentration of C6H5CHO, BTPPC, and NaOH. When the agitating speed is less than 200 rpm, the reaction rate is controlled by diffusion. Uniform mixing of two phases is reached when the agitating speed is greater than 600 rpm. The kinetic data indicated that the reaction rate depends linearly on the concentrations of NaOH and BTPPC and asymptotically on C6H5CHO concentration. The reaction is very rapid and is complete within a few minutes, even at 0°C. The yield of stilbene as high as 95% can easily be obtained. The cis- to trans-isomer ratio in the stilbene product is about 2, independent of reactant concentrations and temperature. A simplified reaction mechanism is proposed to rationalize the kinetic data.