In this paper,FTIR has been applied to the investigation of the tumor cell of mouse transplanted tissue injured by PDT (Photodynamic Therapy).Experimental results show that the characteristic bands of nucleic acid,protein,and lipid changed to different extents,resulting in decreasing of peak and frequency shift to higher wave number or lower wave number.Conclusion:the configuration and conformation of nucleic acid,protein,and lipid changed after PDT acted on tumor tissues.These caused that the DNA strand was induced a cleavage,protein lost activity,and cell membrane function declined.Moreover,the structure and functional of the cell were damaged,leading to cell apoptosis or death.