This dissertation mainly deals with the production and characterization of micro-tubular Solid Oxide Fuel Cells (SOFCs). Such cells not only show like all the other types of high temperature fuel cells a huge flexibility concerning the potential fuels but even more they are able to withstand fast temperature changes. This makes them especially suitable for portable or semi-mobile applications. One main focus of this work was the development of electrolyte- and anode-supported micro-tubular SOFCs and furthermore the improvement of their power densities and long time stabilities. To reach these goals not only the cells themselves had to be improved but also the electrical contacts to the cell. With the help of electrochemical measurements (e.g. impedance spectroscopy) and scanning electron microscopy, it was possible to characterize the dominant losses and/or degradation processes. The results facilitated a well targeted materials improvement and in consequence of this a much better performance cell. Because of the parallel development and testing of the anode- and electrolyte- supported micro-tubular SOFCs, a comparison concerning their potential for practical application became possible. The anode supported cells (ASCs) showed about 1440 mW/cm at a typical working temperature of 850 °C which was more than three times higher than the value achieved for the electrolyte supported cells (ESCs) at 900 °C. But on the other hand ESCs had a much better redox stability. The second main focus of this work was the testing of potential fuels for micro-tubular SOFCs. For this case fuels for mobile applications like diesel and kerosene reformate and renewable fuels like wood gas from air and steam gasification were investigated. The results of this work e.g. showed that under the testing conditions SOFCs can stand 1 ppm hydrogen sulfide and 5 ppm hydrogen chloride. These results allow a better definition of the limits/goals of wood gas purification for SOFC applications.