Reaction kinetics for the formation of sodium decyl sulfonate from alkyl halide and sodium sulfite in microemulsions based on nonionic surfactant were investigated and compared with those in oil-water two-phase systems. Reactions were run at room temperature at various oil-water ratios. Whereas at room temperature almost no reaction occurred in the two-phase systems. all microemulsion-based reactions proceeded at a fair rate. No clear relationship between microemulsion structure and reaction rate could be seen. An equation describing reaction kinetics in the microemulsion system has been derived based on the pseudophase model.