The chemical structures of three characteristic fractions each isolated from the dormant spore coats of Bacillus megaterium QM B1551 and B. megaterium ATCC 19213 were studied. The paracrystal fractions corresponding to the fibrillar structure of the inner coat composed mainly of keratin-like substance and alkali-soluble fractions consisted of acidic protein (isoelectric point: pH 4) which mainly contained aspartic acid and glutamic acid. No remarkable differences were seen chemically or physically between those fractions isolated from both strains. The resistant fraction corresponding to the outer spore coat of B. megaterium QM B1551 was composed mainly of phosphomucopeptide, but the fraction isolated from B. megaterium ATCC 19213 had a different chemical structure in phosphorus and hexosamine contents.