In recent years, the focus has increasingly shifted towards global warming and the protection of the environment. Regarding the iron and steel industry increasing demands for lower-energy and more environmentally friendly processes arose. To counteract the incidental CO2 emissions and to meet the requirements from policy, the exiting processes for iron production are not sufficient. The development of a hydrogen-based direct reduction process is considered as a promising solution. The focus of this master's thesis was to analyze the reduction behavior of magnetitic and hematitic ultra-fine iron ores under hydrogen at certain temperatures and in case of magnetite to investigate the influence of the oxidation pretreatment prior reduction. A high-pressure thermogravimetric analyzer was used for the reduction experiments. For the reaction gas pure hydrogen and a gas mixture of hydrogen and water vapor was used. The test results revealed that a pre-oxidation of magnetite improves the reducibility. Furthermore, the reduction with the hydrogen / steam gas-mixture takes significantly longer at temperatures below 700 °C compared to pure hydrogen. Using the multi-step kinetic analysis, based on the model developed by the Johnson-Mehl-Avrami, the limiting mechanism during reduction could be identified. The results were confirmed by the images from optical and scanning electron microscope.