The influence of the size of surface seal on direct runoff hydrograph from the catchment observed at the catchment outlet was analysed. The analysis based on 10-seconds rainfall data obtained from the rain-gauging station Zawiła, land use data and information from agricultural soil map. The study was conducted in the Wróblowicki Stream catchment, located in Cracow area. The CN-SCS procedure was used to calculate the effective rainfall. The direct runoff hydrograph was established on the basis of instantaneous unit hydrograph and unit hydrograph for Nash’s model parameters. The calculations were performed for four selected rainfall events, for different sealing degree of the catchment, calculated on the basis of the land use data. It was shown, that the response of the catchment to the same precipitation differs depending on the degree of urbanization. The differences include the amount of effective rainfall, time of its appearance, lag-time, volume of the flood wave and the time of occurance of flood peak. The bigger sealing degree of the catchment, the shorter lag-time, larger volume of the flood wave and shorter time to peak.