Objective: This study focuses on investigating the effects of different methods on the determination of adsorption isotherm of bread and the relationship between moisture content and water activity of bread at 25 ℃. Methods: The water adsorption isotherms of bread at 25 ℃ and in the range of 0.100~0.902 water activity (A_W) were measured by saturated salt solution method (SSS), dynamic water transfer analyzer (DWT) and dynamic vapor adsorption method (DVS), and then seven different kinds of adsorption models were used to fit the results. Results: The adsorption isotherm of the bread belongs to the II curve. Halsey model and Peleg model are the best fitting models for measuring the whole bread adsorption isotherm by SSS method and DWT method respectively. Halsey model and Oswin model were the best fitting models for determining the adsorption isotherms of bread crumb and crust by DVS method. Though the SSS method could not limit the volume and quality of the bread, it is time-consuming and unstable in high-humidity condition. However, the DWT method could provide stable humidity conditions without limiting the volume or the quality of the bread. Compared with the SSS method and the DWT method, the DVS method could obtain the result quickly, but the quality and volume of the bread were limited. The results provide a theoretical basis for the choice of the adsorption isotherm measurement method and the quality control and storage stability of bread. Conclusion: DWT method is more suitable for the determination of bread adsorption isotherm.