E-book is a fast growing service for mobile Internet. A user reads e-books through an e-reader that could be a dedicated reading device or a mobile application on the smartphones or the tablets. With content protection of Digital Right Management (DRM), e-books take longer chapter loading time due to necessary data decryption. This paper propose a mechanism that preloads a small number of chapters into the buffer for DRM-protected e-books. When the user reads a chapter in the buffer, our solution reduces the user waiting time without affecting existing content protection. We also analyze the buffer replacement cost and effects of the limited buffer resource.