The purpose of this investigation is experimental research of many interruption performance for Molded Case Circuit Breaker (MCCB) currently used for the protection of a low voltage circuit. It is anticipated by interruption especially by high current many interruptions that the interruption performance will decrease. In order to investigate the performance change by many interruptions, it is important to grasp an interruption characteristic.The interruption experiment was conducted in large current for many times, and phenomena which are one of factors of the successes or failure of interruption, were observed. By carrying out the numbers of interruption it is shown that post-arc current begins to flow and duration of the arc is ten to a few hundred micro seconds. In order to explore relation between post-arc current and a decrease of an interruption characteristics, experiment conditions of post-arc current was investigated.