A capillary electrophoresis(CE) method for the determination of alendronate was developed by using 4-methoxybenzenesulfonyl chlorine(MOBS-Cl) as a pre-column derivatization reagent.The derivative reaction conditions were investigated,and the optimal derivative conditions were as follows:the alendronate reacted with MOBS-Cl in 20 mmol/L borate buffer solution(pH 11.5),and the molar ratio of alendronate to MOBS-Cl was 1∶10.The temperature for the derivatization reaction was 50 ℃ and the reaction time was 10 min.The separation of the derivatives was achieved on capillary column by using 20 mmol/L borate buffer solution(pH 9.3) at a temperature of 25 ℃ and a separation voltage of 20 kV.The injection was carried out under the pressure of 0.5 psi for 5 s,and the detecting wavelength of diode array(DAD) was 233 nm.The calibration curves were linear in the range of 1.0-400 μg/mL,and the limits of detection were 0.5-1.0 μg/mL.This proposed method was applied in the determination of alendronate in pharmaceutical preparations and urine samples with satisfactory results.