The influence of selected physicochemical factors on the degradation of five PAHs in river water and distilled water was tested. Even in darkness, in distilled water some losses of PAHs were observed, different for various compounds, from 22% to 41% after 21 days. Aeration with air increased the losses of PAHs. But very high degradation was found when samples were irradiated with light, for some PAHs up to 90%. The loss of PAHs in river water occurred much faster then in distilled water. The changes in PAH concentrations in distilled water could be described by first order reaction. The equation was proposed and the half-lives were calculated. In river water two stages of degradation were noticed. The different PAHs showed the different degradation, the fastest process was for benzo[a]pyrene and indeno[c,d]pyrene.