The high temperatures required to operate solid oxide fuel cells (SOFCs) allow for internal reforming of hydrocarbon fuels over a Ni-based anode. With their capability of being fuel flexible, SOFCs have operated under a wide range of fuels including diesel as examined in this study. But in order to reduce high possibilities of deposit formation in diesel internal reforming, additional external reforming technology was used for our system. The final goal of this research is to develop diesel-powered SOFC systems for residential power generation. Before constructing a complete SOFC system, a series of durability experiments were conducted on individual components of the system including the fuel reformer and stack. After testing the full-scale diesel reformer, deposit formation was visible within the catalyst and on the surface of the reactor head, which seriously degraded the performance. With several individual components tested, the construction of one-box type SOFC system is in progress. In a preliminary six-cell stack test using sulfur-free synthetic diesel, the system initially showed an output power of at a 0.8 V average cell potential. However, there was a significant drop off in output power after a few hours of operation, which was likely caused by severe deposit formation on the SOFC stack. Light hydrocarbons such as ethylene and/or “less reformed” heavier hydrocarbons caused by gas reactions under the incomplete fuel mixing upstream of the catalyst were likely responsible for the deposit formation.