Peroral and intravenous administrations of C-14-labeled carboxymethyl-chitin (CM-chitin) revealed that CM-chitin accumulated in bone marrow. Thus, a composite of CM-chitin with hydroxyapatite (HA) was prepared to examine the bone repairing properties by animal and cell line experiments. The new bone formation of CM-chitin.HA composite was superior to that of CM-chitin, HA, and blank. A porous CM-chitin.HA composite is a functional material which could act as a scaffolding of osteoblast-like cells, a barrier to ingrowth of fibrous connective tissues. The cytotoxicity of CM-chitin was evaluated using the MC3T3-E1 cell line, and we found that control of degree of deacetylation is a very important factor in using CM-chitin as bone repairing material.