Photodynamic therapy (PDT) is a treatment for cancer involving three key components: sensitizer, light and tissue oxygen. A sensitizer is a chemical compound that can be excited by light of a specific wavelength. Phthalocyanine ClAlPcS(2), belonging among the promising second generation of sensitizers, was evaluated as an inducer of photodamage on NIH3T3 (mouse fibroblasts), B16 (mouse melanoma), MCF7 (human breast adenocarcinoma) and G361 (human melanoma) cell lines. A semiconductor laser was used as a source for evocation of the photodynamic effect. We report the influence of various concentrations of the sensitizer in combination with laser irradiation on the photodamage of cells. Viability of cells was determined by means of molecular probes (Calcein AM and ethidium homodimer) for fluorescence microscopy. The quantitative changes of cell viability in relation to sensitizer concentrations and laser irradiation were proved by fluorometric measurement. We detected phototoxicity evoked by laser irradiated sensitizer in all studied cell lines. In addition, the viability studies showed that G361 melanoma cells and MCF7 breast adenocarcinoma cells were more sensitive than NIH3T3 mouse fibroblasts and B16 mouse melanoma to photodynamic damage induced by ClAlPcS(2).