A numerical prediction of the transient fuel temperature in an aircraft was made and verified with a flight test. The analysis was studied with the finite difference method. Numerical calculation was performed by an explicit method of the modified Dufort-Frankel scheme. Convective heat transfer coefficients were used in calculating heat transfer between the aircraft surface and the ambient air. For an aircraft on the ground, an empirical equation represented as a function of free-stream air velocity was used. And, the heat transfer coefficient for flat plate turbulent flow suggested by Eckert was employed for in-flight phases. The governing equations used in this analysis are the mass and energy conservation equations on fuel and oils. The analysis was verified with the flight test data of a fuel system with additional fuel supplies and return concept. As a result of the verification, the difference of the fuel temperatures obtained by the analysis from those of the flight test data was relatively small with a tendency to increase in the later phases of the flight.