Stability of Zn(II) and Cu(II) complexes of porphyrin derivatives (pheophytin and mesoporphyrin) to UV-B -irradiation has been studied by absorbance spectroscopy in 95% ethanol. The chosen porphyrins as well as their heavy metal complexes undergo photochemical decomposition obeying first-order kinetics. In general, pheophytin is more stable than mesoporphyrin to UV-B irradiation. On the other hand, stability of Zn(II)-complex is smaller than Cu(II)-complex both for pheophytin and mesoporphyrin; however while Cu(II)-complex with pheophytin is more stable than the one with mesoporphyrin, with Zn(II)-complex the situation is vice versa