Nutritional factors play an important role in skeletal development during growth. However, the absorption rates of many bone-related minerals are relatively low from traditional diets, especially for people in Asia and Africa. In the present study, the effect of marine collagen peptides (MCP) derived from chum salmon (Oncorhynchus keta) skin on the development of femurs in growing rats of both sexes was investigated. MCP supplementation could increase the size, mineral density, dry weight, ash weight, content of most minerals and both stiffness and toughness of femurs in male growing rats. However, such effects were milder in female rats. The reported increase in mineral density was likely to be related to increased osteoblast activity rather than a decreased rate of bone resorption, as an increase in serum osteocalcin and bone-specific alkaline phosphatase content was observed, but no significant difference in serum N-terminal telopeptide of type I collagen compared with control was found. MCP supplementation could promote the development of long bones in growing male rats.