Determination of effect of the leaf area ratio on the results of slope stability calculation of one of the landslide's prone slope of in the Pogórze Wiśnickie was presented in the paper. The calculations were carried out in modules Vadose/W and SLOPE/W of package GeoStudio 2012. The calculations involved the integration of rainfall infiltration process and slope stability calculations. As a result, the calculations allow to determinate precipitation conditions (time and accumulated precipitation height) causing slope failure (i.e. rainfall threshold). The calculation results showed significant impact of LAI on the results of modeling. It was revealed, that LAI values in range 1-3, corresponding to the grass vegetation, contribute in long-term to accumulation of precipitation within slope, which limits its retention ability when intense rainfalls occur. In turn, the leaf are index LAI = 5, corresponding to the coverage of trees, increase the retentive capacity of the soil, which resulting in delayed response of slope on rainfall with in comparison to an area covered with grass plants. It was also found significant impact of moisture content conditions on rainfall threshold. It was revealed that in case of analyzed slope threshold rainfall can be comprised from 90 mm to over 700 mm.