The photodynamic activity of magnesium protoporphyrin IX (MgPpIX) was evaluated.Biomolecule photooxidation and erythrocyte photohemolysis assays were performed. The activities wereevaluated using MgPpIX, oxygen and visible light. The results showed that this protoporphyrin caused thephotooxidation of biomolecules and the photohemolysis of red blood cells. However, the efficiency of MgP-pIX was likely diminished by the aggregate formation, as evidenced by the high value of kd [2.56 ± 0.46(kd/105)]. These factors should stimulate interest in further studies, with the goal of transforming MgPpIX into another alternative for the treatment of cancer and other disease.