Aerobic thermophilic stabilization and degradation of waste activated sludge from wastewater treatment plant was studied. The main parameter of research was the organic fraction reduction (expressed as VSS). The experimental part of the study was divided into two parts. In first, the goal was determination of the most beneficial operating temperature. Batch experiments were, performed at temperatures of 20, 37, 40, 45, 50 and 55 °C. The most beneficial temperature for aerobic digestion of waste activated sludge was found to be 50 °C. The second part of experiments studied the continuous process. Experiments were performed at 50 °C where VSS degradation was studied. It was found that VSS degradation was 29.7% at a retention time of 5 days, and 48.2% at a retention time of 10 days. A simple first order kinetic model was applied. From the batch experiments in the first part the model parameters were calculated. From the parameters calculated from the batch study, the behaviour of the continuous process was predicted. Comparison of model and experimental results showed a very good match for retention times up to 8 days. At retention times above 8 days the experimental data showed better results.