Cancer, which is often described as an uncontrollable rapid proliferation of cells, is currently theleading cause of death in the world together with cardiac disease. Therefore, the main purpose of thecurrent research work was to study the anticancer effects of a first-time-synthesized phthalocyanine (Pc)as photosensitizer in PDT against cancer and evaluate its effects on human cells in vitro. Quantum yields ofsinglet oxygen photogeneration were in air using the relative method with standard-ZnPc as reference andDPBF as chemical quencher for singlet oxygen. The concentration of DPBF was prepared almost 3 x 10-5molar to avoid chain reactions induced by DPBF in the presence of singlet oxygen. Solutions of Pc assensitizer (absorbance = 2.0 at the irradiation wavelength) containing DPBF were prepared in the dark andirradiated in the Q band region using the setup described. DPBF degradation at 417 nm was monitoredwith UV-Vis spectrophotometry. For in vitro studies, nine different MFPc-1 concentrations (0.2 µM- 0.4 µM0.8 µM- 1.6 µM- 3.2 µM- 6.4 µM- 12.8 µM- 25.6 µM- 51.2 µM) applied to MCF-7 and MDA-MB-231 breastcancer cell lines for 24 hours and MTT assay was carried out. After determination of optimumconcentration, mitotic index, and apoptotic index values of cell lines were determined with administrationof these concentrations. Singlet oxygen quantum yield (Φ), which is a measure of the efficiency, of MFPc1 was found 0.50, although MFPc-1 is being metal-free phthalocyanine. For in vitro studies after theapplication of different concentrations to MCF-7 and MDA-MB-231 for 24 hours, the optimum concentrationwas determined as 12 µM for both cell lines by the MTT assay. After application of the determined optimumconcentration for 24, 48 and 72 hours, there was a significant decrease in the mitotic index values andsignificant increase in the apoptotic index values of both MCF-7 and MDA-MB-231 breast cancer cell lines.