The use of recombinant human bone morphogenetic protein-2 (rhBMP-2) to induce ectopic bone formation requires a carrier. Type I atelocollagen, a biomaterial with a porous structure, excellent operational features, and biocompatibility, is an effective carrier for rhBMP-2. However, the conventionally used lyophilized rhBMP-2/collagen mixture does not necessarily give adequate bone-induction effect. In the present study, we examined the effect of immobilizing rhBMP-2 to type I atelocollagen on the cellular activity of ST2 cells. The following results were obtained: (1) rhBMP-2 was effectively immobilized to succinylated type I atelocollagen, indicating the usefulness of succinylated type I atelocollagen in immobilization; (2) studies of alkaline phosphatase activity confirmed the effectiveness of rhBMP-2 immobilized on succinylated atelocollagen in augmenting cellular activity.