In this paper, we suggested an evaluation method of cracks in a ceramic product by resonant ultrasound spectroscopy. For experiment, we manufactured nondestructive measurement system by resonant ultrasound spectroscopy and measured resonance frequencies of acceptable and cracked ferrules. The evaluation criterion of ferrule is based on the comparison of resonance frequencies between acceptable and cracked-ferrule. The criterion value that defined by suggested formula is 2. By using the criterion, it is possible to evaluate both acceptable and cracked-ferrule.