A miniature ammonia cracker, with an overall weight of ≈195g and volume of ≈50cm 3 , has been developed for portable fuel cell power supply. The cracker is composed of a SS-316L tube body, a heating rod and monolithic microfibrous CeO 2 -promoted Ni/Al 2 O 3 catalysts incorporated within the annular housings between the heating rod and the inner wall of the tubular body. The catalyst monolith is obtained by placing CeO 2 and Ni onto the microfibrous carrier consisting of 3.5vol% 8μm diameter nickel fibers and 38vol% 100–200μm Al 2 O 3 particulates through stepwise incipient wetness impregnation method using cerium and nickel nitrate precursors. This cracker shows pleasing operability for high efficiency H 2 production via ammonia cracking with low pressure drop. Roughly 158W equivalents of H 2 can be produced with ammonia conversion of >99.9% at 600°C and 1100 standard cubic centimeter per minute (sccm) ammonia feed gas rate within this cracker through the entire 300h test. Power density and energy density are estimated to be ≈3160W/L and ≈2150Wh/kg, respectively.