In the present paper, NMR spectroscopy, an effective tool to detect the variation in molecular structure and changes in chemical composition of metabolites in tissues, was used to study the differences between malignant and normal tissues from rectum. 1H and 31P spectra of seven malignant rectum tissue samples and five normal control tissues were investigated by using a 300 M NMR spectrometers and compared with the results of the infrared spectra of normal and malignant rectum organ tissues. The results indicate that the 1H and 31P spectra of rectum cancer tissues are significantly different from those of the normal controls and most differences present in the form of variation in relative intensities of the characteristic peaks of various metabolites. Systematic differences in the NMR spectra between malignant tissues and normal controls are as follows: in the 1H NMR spectra, differences lie in fatty acids with the concentration of fatty acid decreasing significantly in malignant tissues. In the 31P NMR spectra, differences lie in phospholipid, with the chemical shift of phospholipid decreasing significantly in malignant tissues. This phenomenon may reflect the fact that the activity of protein synthesis is enhanced in cancerous tissues. The difference in the chemical shift of phospholipid between normal rectal tissue and malignant tissue may be considered as a detection criterion. Therefore, the above spectral variations in 31P NMR spectra may be utilized as a potential tool to diagnose rectum cancer.