Japanese enterprises have tremendous numbers of patents, but the half numbers of patents are not used. In addition, 60 percent of unused patents are considered as defensive patents. However, the enterprises do not have a clear understanding of how the defensive patents are defined and managed. The defensive patent has not yet been clearly defined by prior researchers. Japanese enterprises have various opinions on its definition and utilization. Therefore, in this study we performed a questionnaire survey for the top 200 Japanese enterprises which have high numbers of patents. According to our survey, about 90 percent of enterprises think that defensive patents are necessary; and the way of thinking that the a defensive patent 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 that the enterprises continue 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.