As one approach to explore unknown nature and utilization of food materials, the authors previously reported on an acid-soluble polysaccharide prepared from alkaline extraction of bamboo leaves, which showed noted suppression on mouse tumor growth. Another polysaccharide which manifested antitumor effect was now prepared from commercial "xylan" extracted from bran with alkali. It remarkably inhibited the growth of Sarcoma 180 in mice tumor. As the polysaccharide consisted of 90% xylose and 10% arabinose, it seems reasonable to name this arabinoxylan. To elucidate the mechanism of anticancer action, reactivity of arabinoxylan with deoxyribonucleic acid (DNA), was examined. DNA was co-precipitated with this xylan by ethanol. On the other hand, the arabinoxylan prevented the precipitation of DNA by perchloric acid. These results suggest that a kind of complex would be formed between DNA and arabinoxylan in the solution.