Driven by the current green building standards, previous studies focused much more on energy efficiency (especially the operation phase) than greenhouse gas (GHG) emission reduction during the life cycle of buildings. Few studies adopted a life cycle measure to assess GHG emission reduction performance of green buildings. The relationship between GHG emission reduction and defined green buildings remained unclear. The authors first develop a life-cycle GHG measure with its definitions. Two state-of-the-art green buildings located in China and Australia are studied to present the relationship between low GHG buildings and green buildings. It is found that although defined green buildings could have better GHG emission reduction performance than conventional buildings because of the excellent energy performance, and sometimes can even achieve the goal of Net Zero Emission Building, green buildings do not necessarily indicate low GHG buildings from the life-cycle perspective. The main reason is that the criteria for green building rating tools usually don't include GHG emission performance. Perusing sustainability, the authors suggest that life-cycle GHG emission reduction should be taken into account in the evaluation of green buildings. This paper outlines the suggestions on improving the green building rating tools to encourage GHG emission reduction performance of green buildings. (C) 2015 Elsevier Ltd. All rights reserved.