A fuel for a fuel cell system, which comprises at least 5 vol. % of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the total content of hydrocarbon compounds which have carbon numbers of 7 and 8 is 20 vol. % or more based on the whole hydrocarbons and the total content of hydrocarbon compounds which have carbon numbers of 10 or more is 20 vol. % or less based on the whole hydrocarbons, and a fuel for a fuel cell system, which comprises at least 5 vol. % of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the fuel has distillation properties; the initial boiling point in distillation of over 40.degree. C. and 100.degree. C. or lower, the 10 vol. % distillation temperature of over 50.degree. C. and 120.degree. C. or lower, the 90 vol. % distillation temperature of 110.degree. C. or higher and 180.degree. C. or lower, and the final boiling point in distillation of 130.degree. C. or higher and 210.degree. C. or lower. The fuel for a fuel cell system has a high power generation quantity per weight, a high power generation quantity per CO.sub.2 emission, a low fuel consumption, a small quantity of evaporative gas (evapo-emission), small deterioration of a fuel cell system comprising such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks and the like to maintain the initial performances for a long duration, good handling properties in view of storage stability and inflammability, and a low preheating energy.