Poly(N-acetylaniline)/poly(4-styrenesulfonic acid-co-maleic acid) (PNAANI/PSSMA) composite film was prepared by cyclic voltarnmetry (CV), and was characterized by FTIR and X-ray photoelectron spectrum (XPS). The electroactivity of the composite film was high in neutral and basic solutions, and it had been used for amperometric determination of ascorbic acid (AA). Compared with pure PNAANI film, the catalytic activity of the composite film was much better. AA was detected amperometrically in sodium citrate buffer at a potential of 0.3 V (versus SCE). The response current was proportional to the concentration of ascorbic acid in the rany of 4.7 X 10(-6) to 5.0 X 10(-5) M and 5.0 X 10(-5) to 2.5 X 10(-3) M, respectively, with the detection limit of 1.9 X 10(-6) mol L-1 at a signal to noise ratio 3. In addition, the stability and reusability of the composite film were performed well, and it was satisfying to be used for determination of AA in real fruit juice samples. (c) 2008 Wiley Periodicals, Inc.