There is provided a rheumatoid arthritis inhibitor for oral intake that has an inhibitory effect on rheumatoid arthritis and is excellent in safety. The rheumatoid arthritis inhibitor for oral intake of the present invention contains, as an active component, a casein hydrolysate containing free amino acids and peptides obtained by hydrolyzing animal milk casein to have an average chain length of not longer than 2.1 in terms of the number of amino acid residues, or a mixture of free amino acids and peptides contained in the hydrolysate.
