The paper presents results of shallow landslides research located in Siary near Gorlice in June of 2010. In the frame of investigations were done in-situ tests including evaluation of geologic- engineering condition near the landslides and laboratory tests including determination of geotechnical properties of soils (grain-size distribution, Atterbergs' limits, shear strength parameters). The main part of paper included analysis of infiltration process and its influence on stability of slope. There were used two methods describing water flow through unsaturated soil: piston model of Lumb and Montrasio-Valentino model. Tests and slope stability analysis results proved that main factor controlling failure of analyzed parts of slope were very intense rainfall, which caused saturation of superficial slope layer built of gravelly silt. The another factor which contributed to saturation were impermeable soil layer of cohesive soil. Integrated infiltration and slope stability calculation results using Montrasio-Valentino model revealed its sensitivity on K parameter, which describes drainage capability of soil. It was indicated that K parameter can be interpreted as function of coefficient of permeability. Slope stability calculations made using Montrasio-Valentino model in analyzed case gave less values of stability factors than the ones based of infiltration calculations using piston flow model.