The Soil and Water Assessment Tool (SWAT) is a physically based watershed scale model, most widely used in many studies focused on predicting, over different periods of time, the impact of water, sediment and nutrients taking into account different land management in gauged or ungauged watersheds. The purpose of this study is to assess the SWAT model performance in a small mountain forested watershed, from the central part of Romania (Tărlungul Mare upstream Tesla). Using the SWAT-CUP (Calibration and Uncertainty Program) and the SUFI-2 algorithm (Sequential Uncertainty Fitting) was conducted a sensitive analysis of the parameters, and the calibration and validation of the SWAT model. The model obtained a good performance in simulating discharges compared to the measured ones. To assess the degree of uncertainty of the SWAT model results for the studied watershed were used the p and r factors. According to the literature, the values obtained for those factors indicate a low level of uncertainty in regards to the model's results and high performance in simulations. Therefore, based on the good performance of the SWAT model obtained for our study case, we can conclude that, depending of the accuracy of the input data, the model can be successfully applied in small river basins to assess the dynamics of hydrological processes and various land use and climate scenarios, this also represents the future research directions of this study. In addition, this work could bring an important support for stakeholders and decision makers in adopting coherent strategies for a sustainable management of small forested ungauged watersheds.