In the present study, a mathematical model was developed to predict the interaction of biochemical oxygen demand (BOD) and dissolved oxygen (DO). The effects ofreaeration source, sediment oxygen sink were added to the model to reflect natural conditions in lakes, rivers. Calibration and validation of the model were conducted by comparison with data obtained from a multi-channel DO-meter. The obtained results showed a good linear relationship between simulated and measured DO values with the correlation coefficients (R2) to be 0.90 and 0.92 for the model calibration and the model validation, respectively. Simulation results also revealed that sediment layer had a significant impact on the DO concentrations in the water. Parameters which significantly affected to the DO concentration modelling are diffusion coefficients of DO, BOD (Db D2) and rate constant of oxygen consumption by the BOD (k2).