Abstract: The kinetics of singlet oxygen phosphorescence in HeLa cells suspended in phosphate buffered saline (PBS) being generated under photosensitized excitation with Radachlorin photosensitizer has been observed and studied. The characteristic time of singlet oxygen generation and its lifetime in HeLa cells have been determined. The experimental data analysis demonstrated that the singlet oxygen lifetime in cells decreases as compared to that in Radachlorin solutions in PBS and in water, while the photosensitizer triplet state lifetime increases.