Photodynamic therapy uses the interaction of sensitizers and light to destroy cancerous cells and tumors. The photochemical interactions of sensitizer, light, and molecular oxygen produce singlet oxygen and other forms of active oxygen, such as peroxide, hydroxyl radical and superoxide ion. The cellular effects include membrane damage, mitochondrial damage and DNA damage. We report the production of reactive oxygen species and the phototoxicity of photodynamic sensitizer palladium(II) meso-tetrakis(4-sulfonatophenyl)porphyrin (PdTPPS4) on human lung cancer cell lines A549. The light emitting diodes (LEDs) were used as a source for evocation of the photodynamic effect. We investigate the concentration dose dependency of sensitizer in combination with LEDs irradiation on photodamage of cancer cells by in vitro methods. Viability of cells was determined by MTT assay. The quantitative changes of cell viability in relation to sensitizer concentrations and irradiation doses were proved by fluorometric measurement. A549 cells are sensitive to photodynamic damage and our results indicate decrease of viability and time-course of ROS production within A549 cells during photodynamic therapy in vitro.