A 500 W SOFC stack provided by Topsoe Fuel Cells A/S was run with reformed diesel fuel for 1,200 h. Diesel fuel used was Swedish Environmental Class 1 containing <10 ppm of sulfur. The fuel was reformed with an autothermal reformer (ATR). The reformer consisted of a mixing chamber and a reactor chamber containing a noble metal catalyst provided by SüdChemie. The reformer used the diesel fuel without any pre‐treatment such as sulfur adsorbent. The reformer unit was able to achieve high conversion of reactants with only ppm levels of higher hydrocarbons at the reformer outlet. Particulate emissions of the reformer were measured to be 30 μg m–3, a very low value even below daily exposure limits in ambient air set by the European Comission directives. The stack was first run with 3% humidified H2 + N2 fuel to obtain baseline performance and then switched to reformate. Diesel reformate was found not to induce significantly more long‐term degradation on the stack compared to hydrogen case. However, an initial degradation of about 20 mV cell–1 was observed during the first 150 h on diesel fuel reformate. This could be an indication of a poisoning mechanism taking place, but needs further research to be verified.