Morphological and hydrological analyses of the characteristics of the Serbian border zone towards Bulgaria were performed. The morphological analysis included the mountain (Stara Planina, Tupižnica, Svrljiške Planine, Suva Planina and Vidlič), structural basin (Zaječar, Knjaževac, Svrljig and Bela Palanka) and valley (Veliki Timok, Beli Timok, Visočica, Dragovištica) parts. Within the hydrological analysis, the areas with the highest and lowest annual amount of precipitation were identified, as well as the hottest and coldest areas. The change of river basins runoff was analysed, as well as the distribution of waters throughout the year in the studied area. The most important elements of the water balance were shown and the hydrological characteristics of the karst terrain were analysed.