Boshin-Kak Bell, which is one of the largest bells, is located at Chong-Ro Square in the center of Seoul. The bell has been struct early morning and late evening for time-report since the 14th century in Lee Era. Therefore Boshin-Kak Bell has been an intimate old friend of Seoul citizen more than 500 years. Unfortunately, motal large cracks were found inside this bell in the horizontal and vertical directions in 1979. The present paper has investigated the propagated bell-crack by ultrasonic flaw detecting method, and the stress level, bell vibration and weight measurement by electric wire resistance strain gauge method. The results indicate that they are useful for further study of Korean bell by nondestructive test.