Abstract: Highly flexible chitosan films were prepared by film casting of chitosan solutions by using lactic acid solutions as the solvents compare to acetic acid solution. Influences of chitosan molecular weights (100 and 740 kDa), lactic acid concentrations (1.0, 1.5 and 2.0% w/v) and lactic acid configurations (L- and DL-forms) on film characteristics were investigated. Fourier transform infrared (FTIR) spectra of the films showed that there were intermolecular bonds between chitosan film matrices and lactic acids. Tensile strengths at break of the films decreased and percent elongations increased when the lactic acid was used instead of acetic acid for dissolving chitosan. Flexibility of the chitosan films increased with the lactic acid ratio for the both L- and DL-lactic acids. The L-lactic acid showed higher plasticization effect than the DL-lactic acid. Film transparency did not change, whereas wetability of the chitosan films increased as the lactic acid ratio increased.