Light in the near-IR (NIR) spectral region can penetrate relatively deep into soft tissue. In this region, the light absorption property is determined by tissue constituents, especially water, fat, and collagen, and their combination ratio. If the light absorption spectra of tissue constituents were known, the combination ratio could be determined by quantifying the light path length in different tissue constituents. In order to obtain the accurate absorption property, the absorption spectra were measured by a Shimadzu 3101-PC spectrophotometer. Since animal fat contains many kinds of fatty acid, five kinds of major fatty acid found in human fat were mixed with proper ratio as a standard sample. The results show that temperature has a stronger effect on the absorption property of water than on that of fatty acid mixture. The absorption spectrum of hog eye lens was measured to obtain the absorption property of collagen. Its absorption spectrum is quite similar to that of dry bovine gelatin. NIR spectroscopy might be useful to characterize or identify different types of soft tissue based on their major chemical composition, such as detecting a fat plaque in a muscular tissue or a tumor in a high fat content tissue.