Silk sericin protein was hydrolyzed by seven proteolytic enzymes in order to examine the effectiveness of the hydrolysates in binding calcium. The amino acid nitrogen content of hydrolysates from Flavourzyme was higher than that for other enzymes, and its calcium binding capacity showed a dose-dependent increase. We examined the effects of calcium binding peptide from sericin hydolysates on the bioavailability of Ca-deficient rats. Three-week-old male rats were fed an Ca-deficient diet for three weeks. Rats were divided into four groups (DD: non-treated group on calcium deficient diet; DD+MC: milk-calcium treated group; DD+OC: organic calcium made using sericin hydolysates; and DD+IC: inorganic calcium ($CaCl_2$). After oral administration of calcium supplements for one week, the calcium content of the serum and liver were significantly higher in DD+OC ($101.7{mu}g$/mL and $49.3{mu}g$/mL) and DD+MC ($83.6{mu}g$/mL and $42.8{mu}g$/mL) than DD ($86.3{mu}g$/mL and $43.4{mu}g$/mL). The alkaline phosphatase (ALP) content in the treated groups was significantly lower than DD, but no significant difference among groups was shown. Aspartate aminotransferase (AST) levels did not show any significant difference between groups. Alanine aminotransferase (ALT) levels were significantly reduced compared to the DD group. In conclusion, binding calcium to peptides from sericin hydrolysates seems to improve its bioavailability, and to hasten the cure of calcium deficiency in experimental rats.