Abstract: Desorption and adsorption isotherms of rice starch powders were determined by gravimetric method and water activity ranging from 0.11 to 0.90 at 25℃ based on adsorption theory. Seven models were used to fit experimental data by linear regression analysis method to ascertain the best of fit. Comparisons were evaluated with the coefficient of determination (R2) , residual sum of squares (RSS) , mean relative percentage error (MRD) and root mean square error (RMSE) . Results indicated that desorption and adsorption isotherms were belong to type II behavior and the hysteresis loop was of type H3according to the classification of IUPAC. Henderson model, Oswin model and GAB model were suitable for fitting the moisture sorption isotherm of rice starch, but GAB model was the best fitted.The parameters X0, C and K of GAB fitting desorption isotherm of rice starch were 0.0800, 36.43 and 0.7646 respectively, and those for adsorption isotherm were 0.0743, 26.87 and 0.7842.