Five kinds of hard biscuits, containing 0-7.2% of the petroleum yeast and other materials such as wheat flour, margarine enriched with vitamin A and D, sugar, common salt and calcium carbonate were prepared. Feeding experiment of young albino rats fed on these biscuits was carried on. The growth ratio and feed efficiency of each group of animals have increased parallel with the content of the yeast. The digestibility coefficient of each biscuit was determined by using albino rats. About 97% of the organic matter and 86% of the protein in the biscuits containing 7.2% of the yeast were digested.