The object of this research was to investigate whether a thyroid cartilage defect can be repaired by newly formed bone induced by bovine bone morphogenetic protein (bBMP). Bilateral thyroid cartilage defects measuring 0.5 × 0.6 cm were created in 25 adult rabbits. Experimental defects were implanted with ceramic bone particles combined with bBMP, or in controls, without bBMP. The animals were painlessly killed at 2,4,8,12, and 16 weeks after implantation. The tissue responses were analyzed by routine histologic examination. An increase in the amount of new bone was observed in the interval from 4 to 12 weeks, and the defects were completely filled with new bone at 16 weeks, in contrast to a minimal new cartilage formation at the defect edges in controls. The results indicate that cartilage defects can be repaired by inducing new bone formation from mesenchymal cells in both perichondrium and muscular fascia.