Thermal changes and their differences on the optical properties of human benign prostatic hyperplasia (BPH) tissues at 808 nm- and 980 nm-diode laser were study in vitro. The measurements were performed using a double-integrating-sphere setup, and the optical properties of BPH tissue were assessed from these measurements using the inverse adding-doubling method. The results of measurement showed that the absorption coefficients, reduced scattering coefficients and optical penetration depths of BPH tissues at 808 nm and 980 nm varied with a change of exposure temperature by thermal effect. In temperature range from 20 ℃ to 80 ℃, the absorption and reduced scattering coefficients of BPH tissue at 808 nm were obviously bigger than that those of BPH tissue at 980 nm, respectively, and the optical penetration depths of BPH tissue at 808 nm were obviously smaller than those of BPH tissue at 980 nm. Maximal absorption coefficients of BPH tissue at 808 nm and 980 nm were respectively 0.528 mm-1 and 0.448 mm-1 at exposure temperature of 20 ℃, and minimal absorption coefficients were respectively 0.436 mm-1 and 0.326 mm-1 at exposure temperature of 50 ℃ and 70 ℃, respectively, maximal difference in the absorption coefficients between 808 nm and 980 nm was 34.1% at exposure temperature of 70 ℃. Maximal reduced scattering coefficients of BPH tissue at 808 nm and 980 nm were respectively 1.45 mm-1 and 1.43 mm-1 at exposure temperature of 80 ℃, and minimal reduced scattering coefficients were respectively 1.15 mm-1 and 0.973 mm-1 at exposure temperature of 20 ℃ and 70 ℃, respectively, maximal difference in the reduced scattering coefficients between 808 nm and 980 nm was 24.4% at exposure temperature of 70 ℃. Maximal optical penetration depths of BPH tissue at 808 nm and 980 nm were respectively 0.684 mm and 0.887 mm at exposure temperature of 50 ℃ and 70 ℃, and minimal optical penetration depths were respectively 0.608 nm and 0.696 mm at 80 ℃, respectively, maximal difference in the optical penetration depths between 808 nm and 980 nm was 30.4% at exposure temperature of 70 ℃. BPH tissues arrived at complete coagulation by heat effect at exposure temperature of 70 ℃, at this point, the differences in the absorption coefficients, reduced scattering coefficients and optical penetration depths between 808 nm and 980 nm were maximal.