A CE/biosensor for measuring ascorbic acid was developed by coupling a polyaniline optical sensor and capillary electrophoresis (CE). The capillary column was partially modified with a thin film of polyaniline redox sensitive material. Ascorbic acid was detected by monitoring the changes in optical absorbance occurring to the polyaniline film upon the reduction reaction. The sensor response (change in optical absorbance at 650 nm) is proportional to the concentration of ascorbic acid over a range of 2.5-250 mg/L and the response range has shown a clear dependence on the characteristics of the polymerized film. High specificity and sensitivity of the present method, low sample consumption, short times of response (ca. 2 min) and the reproducibility of the results demonstrate that the CE/polyaniline-sensor could be further employed in the study of the relation between the content of L-ascorbic acid in body fluids and clinical parameters, e.g., cell ageing.