Fuel cell is one of the most promising clean energy and alternative energy technologies due to its advantages of low emissions and high efficiency. One application of the fuel cell technology is onboard auxiliary power units (APUs) for power generation in aircrafts, ships, and automobiles. In order to supply hydrogen or syngas for the fuel cell APUs, onboard fuel processing technology was proposed to convert hydrocarbon fuels into syngas through reforming reactions. Two major tasks need to be completed in onboard fuel processing technology. Firstly sulfur compounds have to be removed from hydrocarbon fuels because sulfur can cause reforming catalyst deactivation and fuel cell electrodes poisoning problems. Secondly hydrogen and carbon monoxide shall be produced by reforming of hydrocarbon fuels at a high energy conversion efficiency. This dissertation focused on onboard fuel processing of Jet-A fuel to produce hydrogen and syngas for solid oxide fuel cell (SOFC) APUs. Jet-A fuel was studied because it is the logistic fuel commonly used for civilian airplanes and military heavy duty trucks. Ultra-deep adsorptive desulfurization of Jet-A fuel from over 1,000 ppmw to below 50 ppmw, and autothermal reforming of n-dodecane as a Jet-A fuel surrogate as well as the real desulfurized Jet-A fuel to produce syngas have been systematically investigated in the present study. For the adsorptive desulfurization of Jet-A fuel, a novel NiO-CeO₂/A1₂O₃-SiO₂ adsorbent was proposed and prepared in-house for experimental tests. The sulfur adsorption kinetic characteristic and isotherm at equilibrium were studied in batch tests, and the dynamic desulfurization performance of the adsorbent was investigated in fixed bed tests. Fixed bed tests operation conditions including liquid hourly space velocity (LHSV), adsorbent particle size, and fixed bed dimensions were optimized to achieve the highest adsorbent sulfur adsorption capacity. For the reforming of Jet-A fuel, autothermal reforming (ATR) method was employed and a bimetallic NiO-Rh catalyst was synthesized for the ATR reactions. A lab-scale 2.5 kWt autothermal reforming system including the reformer and balance-of-plant was designed, fabricated, integrated and tested. The reforming system performances at various operation conditions were compared. Reformer operation temperature, steam to carbon ratio and oxygen to carbon ratio, as well as pre-heating temperatures for fuel, air and steam were optimized based on system energy conversion efficiency, H₂ selectivity and COₓ selectivity.