In this work the temperature dependence of heterogeneous nucleation of n-nonane vapor on sodium chloride seed particles was investigated. Nucleation is a statistical process of particle production from the vapor phase. In the case of heterogeneous nucleation the particles do not form spontaneously from the vapor phase but with help of a so-called seed particle. Previous experiments focusing on the temperature dependence of the process have shown a temperature trend opposite to the one predicted by the Kelvin equation and the Fletcher theory. The aim of the measurements was to determine the dependence of activation probability on the saturation ratio. Much effort was put on the attempt to measure the activation probability curves at constant temperature as it forms a basis for further evaluations. Activation probability curves were determined for three different seed particle diameters (7nm, 10nm and 15nm) and temperatures (-10°C, 0°C and +10°C). Experimental data did not show a clear temperature trend whereas theoretical calculations based on the classical nucleation theory predict smaller onset saturation ratios for higher temperatures. The observations seem to suggest that the classical nucleation theory does not consider all processes that play a role in heterogeneous nucleation.