The electron cyclotron resonance microwave discharge ion thruster μ10, which was installed in Hayabusa, has experienced an autonomous stop in the final phase of Hayabusa project by the degradation of the neutralizer. It was shown that the neutralizer is a critical element that limits the thruster lifetime. The objective of this study is to understand the mechanism of performance degradation of the neutralizer and to find out the methods to extend the lifetime of neutralizers. We presupposed a degradation mechanism by studying the neutralizer which had gone through a 20,000-hour endurance test and whose degradation had already occurred. According to this mechanism, it is expected that to increase sputtering resistance against divalent xenon ions bombardment is effective to enhance endurance. In this paper, we verify the effectiveness of increasing sputtering resistance using molybdenum covering by additional endurance tests.