Instability phenomena, i.e., landslides, are among the common problems in practical geotehnical engineering. Objective of this work is to test the activity of clays in colluvial deposits of several landslides, to determine whether the clay activity is one of the causes of landslide phenomena in the area of the Dubračina river basin. Dubračina river is the main stream of the Vinodol valley, which is situated in the Primorsko-goranska county. Field investigations were conducted on several locations in area of the Dubračina river basin. Samples were taken from colluvial deposits of several landslides. Particle size distribution and consistency limit ( i.e., liqid and plasticity limits) were detemined from laboratory tests. Soils were classified according to European Soil Classification System (ESCS), and clay activity was determined according to statement that defines it as correlation between index of plasticity and clay fraction distribution. Colluvial deposits are mostly composed of inactive clay minerals, i.e.,kaolinite,and of normal clay minerals, i.e., illite. Active clay minerals from smectite group, i.e., montmorillonite, has been found in only one soil sample. According to the given results, activity of clay minerals from tested colluvial deposits can not be directy considered as one of the direct causes of landslides.