In this study, at first, different free and four fee book-based Digital Libraries (DLs), available via www were reviewed. Four DLs Gutenberg, 24×7, Netlibrary and Ebrary were chosen. A comprehensive inventory consisted of general information, search features, display options and unique features was composed for comparing the interfaces of these DLs. Then chosen interfaces were compared and evaluated. Results showed that Netlibrary scored higher according to the specified criteria. However, in designing interface for such DLs, designers should take into considerations all the criteria proposed in this study.