Protease degradation of matrix (Ma) protein and microfibril (Mf) protein, which are the major components of human hair, were investigated. Ma or Mf protein was partially extracted from human hair and four types of keratins were prepared: Ma film, Mf film, Ma-rich fiber, and Mf-rich fiber. Of the two keratin films treated with protease, Mf film showed much higher degradation than Ma film. Of the two keratin fibers treated with protease, Mf-rich fiber showed much higher degradation than Ma-rich fiber. Protease potently degraded Mf protein. Furthermore, there was a high correlation between the extent of degradation and the water absorption of keratins.