A single-integrating sphere system was designed to measure the optical properties of milk.Boundary conditions required for inverse adding-doubling method(IAD) were fully satisfied by using self-made precise collimating system.SNR and measuring accuracy were improved by using dual-beam and modulation of sources.The optical properties of skimmed milk,partly-skimmed milk and pure milk with different brands were obtained at 632.8 nm and 1 064 nm wavelength respectively.And the radial distribution of light with diffusion equation was in good agreement with that measured by the diffuse-reflectance measuring system.