Synthesis of sodium decyl sulfonate in various types of microemulsions based on nonionic surfactants have been reported in our previous paper. As a continuation of this study the effect of ionic surfactants with different counterions on the reaction profile was investigated. As expected, the electrical potential of microemulsion droplets significantly influenced the degree of conversion probably by affecting the diffusion of ionic species into the interfacial region where the reaction occurs. The reaction yield was also highly dependent on the type of counterions. Tetradecyl trimethyl ammonium acetate increased the yield, but sodium dodecyl sulfate and tetradecyl trimethyl ammonium bromide gave decreased conversion. The counterion effect was explained by the competitive association of ions with the surfactant monolayer at the oil/water interface.