The retention behavior of some isomeric mono-substituted phenols was investigated by high-performance liquid chromatography on a RP-C_(18) stationary phase using β-cyclodextrin as mobile phase additives. Effects of methanol content of mobile phase were examined. Effective separations of some isomeric mono-substituted phenols were achieved on a RP-C_(18) stationary phase using β-cyclodextrin as mobile phase additives. Moreover, baseline separations of isomeric nitrophenol and ethylphenol were achieved.