Penicillium chrysogenum strains, isolated from rapeseeds, soybean, and sunflower seeds, were incubated in a liquid medium with rapeseed oil, soybean oil, and sunflower oil added. The effects of water activity (a_w) of the medium (0.995; 0.950; 0.900; 0.850) and temperature (15 and 25 ºC) were studied on the dry mass content of mycelium and on the lipolytic activity. The growth of the mycelium of the strains analyzed varied depending on a_w and temperature. The lipolytic activity at a temperature of 15 ºC was higher than that at a temperature of 25 ºC. The highest lipolytic activity of P. chrysogenum strains was reported at a temperature of 15 ºC at the lowest tested water activity of the culture medium (a_w = 0.850). The results obtained prove that the lipolytic enzymes produced by the strains of that fungus can initiate disadvantageous quality changes in oils, and this is possible even where there is no visible growth of the mycelium.