The MIDREX® process is the dominant process for the production of direct reduced iron. This thesis focuses on the reduction behavior of iron oxide pellets under MIDREX® conditions. Three different case studies were carried out on two different iron oxide pellet grades using two different reducing gas mixtures. The reduction tests were performed using a thermogravimetric method by a fixed bed reactor (with an inner diameter of 75 mm) in a temperature range of 730–890 °C. The data from the experiments were fitted using both single-step kinetic models and a multi-step model to find the limiting mechanism during the reduction from FeO to Fe. However, more than one specific single-step model could fit the experimental data. According to the multi-step model, the reduction of the pellets, depending on the experimental conditions, could be controlled by three mechanisms: (1) chemical reaction on the surface of the iron oxide; (2) diffusion through the metallic iron layer; (3) nucleation of new iron phases within the pellets. The results were confirmed by morphological investigations in different case studies. Furthermore, the apparent activation energy for the reaction was determined to be in the range of 20–55 kJ/mol depending on the test conditions and pellet grade.