Fat are typical and important nutrients of many food systems.From a view of optical measurement,the component plays a vital role in the determination of food optical properties.The optical properties of fat in turbid liquid food systems have been studied in the near-infrared region.A biological fluid of raw milk was firstly selected as a matrix and then a simulation sample for complex liquid food systems was created by adding butter oil to the raw milk matrix.The changes of optical properties with the contents of fat were measured by using the double integrating sphere technology in the wavenumber range from 10000 cm-1 to 6000 cm-1.The results indicated that the absorbance and scattering coefficients changed with the contents of fat.Moreover,bigger changes of the scattering coefficient were induced by the contents of fat,which showed that the scattering effect cannot be ignored.This study provides valuable theory reference for the measurements of turbid liquid food materials by near-infrared spectroscopy.