Forests are influencing surface runoff, provide a protective cover for the landscape and returning a large proportion of precipitation back to the atmosphere. On average, two-thirds of the precipitation that falls on the forested area, returne to the atmosphere through the process of evaporation and transpiration. In the thesis we discussed the impact of forest on runoff in forested basin. In the first part of the thesis we present various factors and the most common findings of researchers about the impact of forest on the hydrological cycle. We also present the individual components of forest hydrological cycle. In the second part we analyze the impact of rainfall interception on the runoff from two small forested experimental basins of Oplotnica River on Pohorje. Both basins are very similar in size and shape, but differ in the position of the catchment area and the structure of the forest. Analysis was conducted on the basis of the measured values of stream flows, throughfall, stemflow and comparison of the structure of forest stands. In the last part of the master thesis we made hydrological models for both river basins, based on the values that were obtained with a preliminary analysis. Model was calibrated and validated. We found out that forest stand has a great impact on the runoff, because smaller stream flow was recorded from the basin with a larger portion of spruce, reflecting the fact that conifer trees intercept more rainfall compared to deciduous trees.