Monitoring the content of nitrate and nitrite plays an important role in the analysis of surface, drinking and wastewaters because it is harmful for health of human. The adsorption of nitrite onto granular activated carbon could be monitored by an on-line spectrophotometric analysis system. artificial neural network modeling has been successfully used to investigate the cause effect relationship in the adsorption process. The artificial neural network model could describe the behavior of the complex interaction process with the range of experimental conditions adopted. Simulation based on the artificial neural network model can estimate the behavior of the process under different conditions.