According to FAO, world milk production has raised to 695 MT in 2009 this report indicate that Iran's participation, with five percent annual growth was 1.2% of world milk production. Dairy plant wastewater categorized as wastewaters with high organic load. The organic load varies according to season and production. Regarding to high organic load and biodegradability of dairy plant wastewater, it is necessary to exist the ability of biological wastewater treatment in the Diary industries wastewater treatment plant facilities. Sequencing batch reactor (SBR) is one of the biological wastewater treatment processes. In SBR biological wastewater treatment operates in sequence of time. In other words, first reactor is filled with influent next mixing and aeration are performed and finally effluent is decanted from reactor after settlement. Nowadays, due to strict regulatory circumstances for quality indexes of wastewater treatment plants effluent, existence treatment plants improvement and more precise design for new plants is required. Modeling is a useful tool for existence wastewater treatment plants improvement and accurate design of new wastewater treatment plants. ASM model is related to modeling Activated Sludge process biochemical reactions and So far no official model has proposed for aerobic biological treatment in SBR. Therefor in this study according to literatures modification of ASM model for SBR biochemical reactions was performed. A laboratory-scale reactor was made for validation of modified model. This reactor was inoculated with activated sludge taken from an aeration tank from Isfahan pegah dairy industry wastewater treatment plant. The reactor shape was cylinder with 50cm height and 20cm diameter. The reactor was operated with sludge age of 5 d, 4 liter volume, a mixed liquor suspended solids (MLSS) concentration 1250 mg/L and sludge volume index (SVI) 100 ml g -1 . The reactor was fed with synthetic diary wastewater (SDW). The synthetic wastewater was prepared by solving industrial milk powder in distillated water. The biochemical model is composed from mathematical expressions of biochemical process rate and stoichiometry coefficients of biochemical process. So a computer program is required for using a biochemical model. In this thesis AQUASIM was used as a software environment. First step in model validation is model calibration. The model was calibrated using respirometry experiments and AQUASIM .next total COD change in the laboratory-scale reactor was measured and the model was run with initial conditions of laboratory-scale reactor then the total COD change in the laboratory-scale was modeled with calibrated model in AQUASIM. For model validation relation between modeling results and measured results was compared with correlation factor. The correlation factor between experimental and modeling results was 0.969. Key Words: SBR, biological treatment, modeling, aerobic treatment, parameter estimation, respirometry