The intrinsic optical parameters absorption coefficient µa, scattering coefficient μs′, anisotropy factor g, and effective scattering coefficient μ were determined for human red blood cell (RBC) suspensions of hematocrit 33.2% dependent on the oxygen saturation (SAT O2) in the wavelength range 250 to 2000 nm, including the range above 1100 nm, about which there are no data available in the literature. Integrating sphere measurements of light transmittance and reflectance in combination with inverse Monte Carlo simulation were carried out for SAT O2 levels of 100 and 0%. In the wavelength range up to 1200 nm, the absorption behavior is determined by the hemoglobin absorption. The spectral range above the cells' absorption shows no dependence on SAT O2 and approximates the absorption of water with values 20 to 30% below the respective values for water. Parameters µs and g are significantly influenced by the SAT O2-induced absorption changes. Above 600 nm, μs decreases continuously from values of 85 mm-1 to values of 30 mm-1 at 2000 nm. The anisotropy factor shows a slight decrease with wavelengths above 600 nm. In the spectral regions of 1450 and 1900 nm where water has local absorption maxima, g shows a significant decrease down to 0.85, whereas μs′ increases.