Pathological changes and thermal coagulation of human liver tissue induced changes of the optical properties of liver tissue at 532 and 1064 nm wavelengths of laser in vitro. The measurements were performed using a double-integrating-sphere setup, and the optical parameters were assessed from these measurements using the inverse adding-doubling method (IAD). The results of measurement showed that the absorption coefficients of normal liver tissues at 532 and 1064 nm are significantly bigger than those of liver tumors at the same wavelength respectively. When liver tissues were coagulated by heat, the absorption coefficients of normal and tumorous liver tissues of thermal coagulation at 532 nm significantly increase, the absorption coefficient of normal liver tissues of thermal coagulation at 1064 nm significantly decreases, and the absorption coefficient of liver tumors of thermal coagulation at 1064 nm significantly increases. The scattering coefficients of normal liver tissue at 532 and 1064 nm are significantly smaller than those of liver tumors at the same wavelength. When liver tissues were coagulated by heat, the scattering coefficients of normal and tumorous liver tissue of thermal coagulation significantly increase. The anisotropy factors of normal liver tissue at 532 and 1064 nm are obviously bigger than those of liver tumors at the same wavelength respectively. When liver tissues were coagulated by heat, the anisotropy factors of normal and tumorous liver tissue of thermal coagulation at 532 and 1064 nm obviously decrease.