Abstract: Photodynamic therapy (PDT), because of its good targeting, minimal invasion, and safety, is becoming a very active area in cancer prevention and treatment, in which the photosensitizers have proved to be the core element for PDT. We developed a new HPLC method for analyzing porphyrin photosensitizers using Shiseido Capcell PAK C18 (150 mm × 4.6 mm, 5 μm) as the column at 30 ℃, methanol-1% aqueous solution of acetic acid as the mobile phase in a flow rate of 1.0 mL·min^-1 in a gradient elution mode, and the detection wavelength at 380 nm. This method, showing good specificity, precision, accuracy and robusty via methodology validations, can be applied to the purity test and assay of porphyrin photosensitizers, and has played a key guide role in the R&D of the new porphyrin photosensitizer — sinoporphyrin sodium.