The correct estimation of river discharge is an important issue in forecasting of drought and floods, designing of water structures, dam reservoir operation and sediment control. For this reason, water resources managers used intelligent techniques such as Artificial Neural Networks and data mining methods such as Decision Tree to reliably estimate the discharge in a river. In this study, the Elman Neural Networks (ENN) and M5 model trees were used to forecast daily discharge of Aharchay River. The daily discharge data of Aharchay River measured at the Orange hydrometric station was used for modeling. The results showed that for the forecasting discharge of one day ahead, the ENN method presents more accurate results in compression with M5 model. For forecasting discharge of one day ahead, the best scenario of ENN model with a relatively complicated structure of 9-3-1 that indicating 9 nodes in input layer, 3 nodes in hidden layer and 1 node in output layer, the calculated error measures were R²=0.90, RMSE=0.028 (m³/s) and MAE=0.001 (m³/s). The corresponding values for M5 model with only two input parameters including the discharge of current and last day, were R²=0.83, RMSE=0.734 (m³/s) and MAE=0.317 (m³/s). Comparing the performance of ENN and M5 models indicated that, however the ENN approach may present more accurate results than the M5 model tree, but the M5 model provides more understandable, applicable and simple linear relation in forecasting daily discharge. In addition, the number of required input parameter for M5 model is less than ENN model. Thus, the M5 model tree can be used as an alternative method in forecasting daily discharge.