Photodynamic therapy has been extensively studied in the last few decades as a potential clinically approved therapy for a broad range of malignant tumors. A main purpose for the treatment of cancer is the discriminating destructive process of malignant cells without damaging healthy tissues. Photodynamic therapy is a photoactivation process of a sensitizer hold on to tumor cells, which generates reactive singlet oxygen species with the ability to wipe out the targeted tumor cells. The mechanisms concerned in explaining the photodynamic therapy of cancer cells annihilation have not been completely recognized. However, recent studies have assisted to clarify the special impacts of photodynamic therapy at tissue, cellular and molecular levels. Porphyrin derivatives have been widely investigated and many other new types of sensitizers have been materialized and verified their efficiency in photodynamic therapy.