Abstract: The scattering and absorption coefficients were determined and compared in vitro for normal and adenomatous human colon mucosa/submucosa, and normal and adenomatous human colon muscle layer/chorion at 630 nm, 680 nm, 720 nm, 780 nm, 810 nm, 850 nm and 890 nm of Ti:S ring laser. Tissue samples were measured with a double integrating sphere set-up to determine their collimated transmission, diffuse reflectance and diffuse transmission at seven laser wavelengths. The inverse adding-doubling algorithm and inverse Monte Carlo simulation were respectively used to calculate the scattering and absorption coefficients from the measurements. The investigative results showed that there were significant differences in the absorption and scattering coefficients between normal and adenomatous human colon tissues per tissue type at the same laser wavelength (P﹤0.01), whether using the inverse adding doubling method or using the inverse Monte Carlo simulation. These large differences of the absolute values in the scattering and absorption coefficients indicate that there were large differences in compositions and structures between normal and adenomatous human colon tissues per tissue type. The scattering coefficients of colon tissues exceed the absorption coefficients by at least three orders of magnitude, and there are the same orders of magnitude in the scattering coefficients for four kinds of colon tissues.