β-CD has a special large molecular cavity with an external hydrophilic and an internal hydrophobic properties,and it could form inclusion complex with 4-tert-octylphenol(OP) and 4-n-nonylphenol(NP)，respectively.In this paper,the stoichiometric ratios and the equilibrium constants between β-CD and the above two alkylphenols(APs) were determined by UV spectrophotometry.The results indicated that OP and NP both form inclusion complexes by a molar ratio of 1∶1 with β-CD, and the equilibrium constants were 71.06 L/mol and 1 402.72 L/mol,respectively.At the same time,the equilibrium constants between β-CD and APs were also studied by capillary electrophoresis under the conditions of 10 mmol/L sodium dihydrogen phosphate-10 mmol/L sodium borate-20 mmol/L sodium cholate(pH 9.0).The double reciprocal was introduced to measure the equilibrium constants,and the values for OP and NP were 68.20 L/mol and 1 357.80 L/mol,respectively.According to F test and t test,the equilibrium constants between β-CD and APs obtained from two methods have no difference.