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Aim. One of the potential methods for treating cancer is photodynamic therapy (PDT), which involves the targeted destruction of cancer cells through the activation of photosensitizers (PS) using light irradiation. The aim of the study was to investigate the photodynamic properties of the squaraine dyes with hydrophilic and hydrophobic substituents. Methods. Fluorescence spectroscopy, UV-VIS spectroscopy, laser scanning confocal microscopy, cytotoxicity assay. Results. It was shown that all studied dyes have maximum absorption in the far-red region, which makes them suitable for PDT. It has been investigated that the squarains can form complexes with proteins, as indicated by changes in their fluorescence. The samples demonstrated minimal dark toxicity but exhibited cytotoxicity after irradiation. The cytotoxic effect of dyes with hydrophilic groups was reduced by binding to BSA. Meanwhile, a dye with hydrophobic substituents shows a photodynamic effect in the presence of albumin. All studied dyes can penetrate through the cellular membrane, stain the cell components in the cytoplasm, and do not accumulate in nuclei. Conclusions. All dyes showed low dark toxicity. However, cytotoxicity increased after irradiation with light of a wavelength of 670 nm. The binding of the dyes with hydrophilic substitutes to albumin negatively impacted their photosensitizing properties. At the same time, the dye with the highest tendency to aggregate exhibited the most significant cytotoxic effect. [ABSTRACT FROM AUTHOR]