Micellar calcium phosphate (MCP), which is a main form in milk, cross-links caseins through their phosphate groups. MCP was separated as the complex with casein phosphopeptide (CPP). Whey calcium, which is separated in a different form from that in bovine milk and used as a calcium ingredient in recent food industry, has superior calcium bioavailability to other calcium ingredients. Growing female rats were fed either MCP-CPP complex or whey calcium as the sole source of calcium for 6 weeks, and the calcium bioavailability was estimated from apparent calcium absorption rate and the bone strength of the femur. The calcium bioavailability of the MCP-CPP complex was significantly higher than that of whey calcium. The higher calcium bioavailability of MCP-CPP complex is due to in part to its solubility in the small intestine.