Because soil erosion which is caused by rain is also an important phenomenon in the Slovak Republic, higher emphasis is impute to research of water erosion caused by rain and that is why we proceeded to calculate the rain factor R. Based on data which were provided by the Slovak Hydrometeorological Insitute for 6 selected meteorological stations in Slovakia, we accomplished to the calculation of rain factor R. For the calculation we used the methodology by Wischmeier-Smith (1978) and results we comparing with the methodology of Hudson (KE> 1) and with already published values of the Research Institute of Soil Science and Conservation. We also created a line exceeded of probability from the calculated data, which gives us detailed information on the occurrence of the calculated R values 1 time per 100, 20, 10, 5, 2 and 1 year. On the basis of calculated data we created a distribution of R factor values for individual months of the growing season and found out that the highest percentage fall on the summer months June, July, August and by contrast the lowest to April and October, so it is necessary to impute emphasis to soil erosion control especially in summer months. Comparing the methodology of Hudson (KE>1) and methodology of Wischemeier-Smith, we found out that the Hudson methodology gives almost 2 times lower value of R-factor than with using the methodology of Wischmeier-Smith.