Abstract: Using 4-methoxybenzenesulfonyl chloride as pre-column derivatizer, and capillary electrophoresis was applied to the determination of hydroxyproline in urine. The optimized conditions found were as follows: ① buffer medium: pH 10.00 of 20 mmol·L-1 boric acid buffer solution (pH 10.00) containing 25 mmol·L-1 SDS; ② temperature of derivatization: 50 ℃; ③ time of derivatization: 15 min; ④ wavelength for UV-detection: 235 nm. Linear relationship between values of peak area and concentration of hydroxyproline was kept in the range of 2.5-200 μmol·L-1, with detection limit (3S/N) of 1.25 μmol·L-1. Precision of the method was tested at the concentration level of 5 mmol·L-1 hydroxyproline for 6 determination, value of RSD found was 2.1%. Recovery of the proposed method was tested by standard addition method, giving values of recovery in the range of 97.8%-103%.