Processes for conveniently and economically producing L-arabinose, enzyme-treated products containing L-arabinose, diet foods and diabetic foods containing L-arabinose with dietary fiber, and fruit or vegetable juices containing L-arabinose are provided. (1) A process for producing L-arabinose by treating a natural material containing arabinan, arabinoxylan or arabinogalactan with an enzyme having an activity of acting on natural substances containing arabinan, arabinoxylan or arabinogalactan and thus releasing L-arabinose to give L-arabinose, characterized in that the above-described natural substance is directly treated with the above-described enzyme without separating or extracting arabinan, arabinoxylan or arabinogalactan. (2) A process for producing a diet food and a diabetic food characterized by comprising treating a dietary fiber material originating in a natural substance containing arabinan, arabinoxylan or arabinogalactan with an enzyme which degrades arabinan, arabinoxylan or arabinogalactan to give an enzyme-treated product containing L-arabinose and dietary fiber, and adding the thus obtained enzyme-treated product to a food. (3) An L-arabinose-containing fruit or vegetable juice characterized by containing an L-arabinose-containing fraction obtained by treating a fruit or vegetable press cake containing arabinan, arabinoxylan or arabinogalactan with an enzyme, and a process for producing the same.