The problem of erosion is very prominent in Mediterranean karst area of Croatia, and one of the reason is the degraded forest ecosystems. The important relationship of soil erosion with the state of vegetation, its degradation stadiums and soil characteristics has been stated. It is widely known that the regression development of vegetation is followed by quick soil erosion, and its progression development causes only normal geologic erosion which is overwhelmed by soil formation. To state the impact of vegetation influence on the intensity of soil erosion by water in preserved and burned stands of Aleppo pine of the karst area of Croatia a forest experiment was made. On two experimental plots of 100 m² (20 x 5 m) during three years, from 2005–2007 the quantity and intensity of rainfall was observed, the surface flow off of rainfall and soil erosion. The results of research of given parameters are shown in this paper. The first experimental plot was set on the burnt area in forest ecosystem of Aleppo pine, GPS coordinates: N 43°33′, E 16°30′. The plot is set on eroded rendsina on marl, 20° inclination, sea level 212 m. The second experimental plot was set in the preserved stand of Aleppo pine of complete stand, GPS coordinates N 43°31′, E 16°32′, on inclination 26° and sea level 227 m. The plot is set on brown soil on marl, which is covered by thick layer of needles. The results show that in the time observed on burnt area 215 rainy days were recorded, out of which the surface flow off and soil erosion were caused in 71 cases. Surface runoff and soil erosion were caused by rainfall from 7.1 mm/m² to 78.6 mm/m². The yearly value of erosion alluvium amounted to 0.1 t/ha, surface runoff 11.30 mm/m², and the coefficient of runoff was from 0.0017 to 0.0824. In the preserved stand of Aleppo pine out of 215 rainy days, 59 were erodible. Surface runoff and soil erosion were caused by rainfall from 8.5 mm to 78.6 mm. Yearly value of erosion alluvium amounted to 0.015 t/ha, surface runoff 5.59mm/m², the coefficient of surface runoff was between 0.0003 to 0.0162.