The unique ability of chlorophyll derivatives to accumulate in tumorous tissues and to cause a photodynamic effect under laser radiation has been successively used in photodynamic therapy. In this connection, enormous research on modifications of the peripheral substituents in chlorophyll has shown that the presence and position of the substituents in the chlorin derivatives make a remarkable difference in biological activity. As a result, we directed our attention to synthesize methyl pheophorbide-a derivatives, chlorophyll-a derivatives, possessing heterocyclic aromatic substituents or pyrazole moieties on the peripheral positions and to examine preliminary in vitro effects of these new derivatives on A549 cancer cells for PDT. From our experimental results, it was observed that the biological effect induced by photosensitizers on cancer cells may also depend upon the chemical structure of the photosensitizers.