Abstract: Objective Fourier transform infrared （FTIR） spectroscopy was applied to observe the postmortem degradation process in mechanical asphyxiated rat’s liver and spleen for providing a new method of estimating PMI. Methods Rats were sacrificed by mechanical asphyxia and cadavers were kept at （20±2） ℃ in a control chamber. The liver and spleen were sub-sampled from the same rat at intervals of 0-15 days postmortem and the data were measured by FTIR spectrometer. The different absorbance （A） ratios of peaks were calculated and the curve estimation analysis between absorbance ratios （x） and PMI （y） were performed to establish mathematical models by the statistical software. Results The band absorbance ratios showed increase, decrease and stable with PMI. The cubic model functions showed the strongest correlation coefficient. Compared with the spleen, the liver showed a higher correlation coefficient. The A_{1 541}/A_{1 396} of liver showed the highest correlation coefficient（r=0.966）. After 6-7 days postmortem, band absorbance ratios showed a steady period. Conclusion FTIR spectroscopy can be a new and efficient method to estimate PMI within 7 days.

Key words: forensic pathology, asphyxia, spectroscopy, Fourier transform infrared, liver, spleen, postmortem interval, rats