A kinetic study of the Wittig reaction for synthesizing stilbene is carried out by reacting benzaldehyde (C6H5CHO) with benzyltri‐phenylphosphonium bromide (BTPPB) in the NaOH(aq)/CH2Cl2(org) two‐phase reaction system. The rate of reaction depends on the agitation speed, the temperature and the concentrations of C6H5CHO, BTPPB, and NaOH. When the agitation speed is low, the reaction is highly affected by interface diffusion. The reactant rate constant, based on theSN2 substitution mechanism and the activation energy are also determined. It is found that the activation energy obtained from the present study (Ea=11.97 kcal/mole) is less than that of the previously documented data (Ea=12.984 kcal/mole) in which benzyltriphenylphosphonium chloride (BTPPC) was used as a phase transfer catalyst.