We report on the characterization of photodarkening (PD) kinetics of Yb-doped fiber samples in a wide temperature range from 77 to 773K and with respect to different Yb2O3 concentrations from 0.09 up to 0:68 mol%. The thermal dependency of important PD parameters is presented for a uniform Yb inversion of about 0.46. We have found out that PD kinetics is affected remarkably by temperature during pumping and that PD saturation is an equilibrium of optical and thermal processes, achieved after passing a loss maximum. The saturated loss for time tending to infinity obviously depends on the fiber temperature.