An Al-containing ordered alloy, NiAl(110), was oxidized under various conditions of ultra high vacuum. The crystallinity and thickness of the formed alumina films were evaluated. The two-step growth process, where a specimen was oxidized at about 600 K being followed by annealing at ca. 1100 K, is well known. We examined the effect of oxygen pressure, substrate temperature and annealing conditions. A one-step process, where a specimen was oxidized at around annealing temperature so that oxidation and crystallization proceeded simultaneously, has been newly developed. The effects of oxygen pressure and substrate temperature in the one-step growth were clarified. It was revealed that a flat well-ordered alumina film thicker than 0.5 nm (known) could be grown by this new method.