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Japanese enterprises have tremendous number of patents, but the half numbers of patents aren't used. In addition, 60% of unused patents are considered as “defensive patents”. However, the enterprises don't have clear understandings on the defensive patents how it's defined and managed. The defensive patent hasn't yet been clearly defined by prior researchers. And Japanese enterprises have various opinions on its definition and utilization. Therefore, in this study, we performed a questionnaire survey to top 200 Japanese enterprises which have high number of patents. According to our survey, about 90% of enterprises think that defensive patents are necessary, and the way of thinking that the defensive patents can be utilized with its role as defending tools against competitors, has been well penetrated to most of the enterprises which made responses to our survey. So, we clarified the features of defensive patents from two aspects which are “the evaluation of the patent” and “the relation to the environment and the strategy”. Furthermore, we recommend for the enterprises to keep managing patents according to the features. The purposes of defensive patents have been also clarified with our survey. There are mainly four reasons why Japanese enterprises have defensive patents.