In response to the increasing severity of environmental pollution, the energy-efficient designs that minimize carbon emissions have been increasingly discussed. After the increasing adoption of Building Information Modeling(BIM), various domestic and international attempts for BIM-based energy performance assessments have been investigated, but most of them have generated various problems from the lack of data interoperability. It makes users inefficient with inputting again the building information which are not compatible at energy analysis phase. Also through energy analysis, the feed-back of results can not be applied bidirectionally for back to the early modeling phase. The purpose of this study is to suggest improvement of interoperability for open BIM-based building energy assessment through object library system. To achieve this purpose, the authors have constructed the object material library based on ASHRAE Handbook reflected domestic material classification system and developed module for pre-checking and modification of material information in energy performance assessment. This study could reduce confusions from different processes and environments and offer the confidence to user. Furthermore as the alternative to lack of data interoperability, the object material library applied domestic state and ASHRAE Handbook can be reliable.