Roll casting of Al-25mass%Si hyper eutectic aluminum alloy strip was tried by an unequal diameter twin roll caster. The casting speed was 10m/min. The thickness of the strip was about 2mm. The eutectic Si and primary crystallized Si were very fine by the effect of the rapid solidification. The size of the primary crystallized Si was not uniform at the thickness direction. The primary crystallized Si at the near surface was finer than that of inside. The eutectic Si was finer than 2μm. The strip could be cold rolled after hot rolling and annealing.