The effect of temperature (4-50 degrees C, relative humidity (RH, 40-80%), and storage period (3-9 days) on the mechanical properties such as tensile strength (TS), percent elongation (%E) and modulus of elasticity (ME) of biodegradable chitosan film was studied by applying response surface methodology and Box-Behnken design of experiment. The results of ANOVA indicated that all the independent variables exhibited significant effect on the film properties. Temperature and RH exerted greater influence on TS and %E, while storage period showed moderate influence. Both linear and quadratic terms exerted significant (p < 0.01) effect, but total quadratic effect (p < 0.01) dominated over the total linear effect (p < 0.01).Simultaneous optimization by desirability approach was carried out on the independent variables to get the optimum levels within the experimental conditions. It was found that at 20 degrees C, 40% RH and a storage period of similar to 7 days, the optimum values for TS, %E and ME were 35.8 MPa, 29.9% and 896.7 MPa, respectively. The predicted responses were validated and the difference between the predicted and experimental responses was not significantly different (p < 0.05). (c) 2006 Elsevier Ltd. All rights reserved.