Mixed-use developments are growing rapidly worldwide in recent years. This emerging establishment combines multiple income producing uses within a building or a group of integrated buildings. Under the concept of compact city and sustainable development, the advantages for mixed-use developments are providing users greatest variety and convenience, fulfilling a live-work-play environment. Nevertheless, from the perspectives of property appraisers and developers, there are limit consensus on the Highest and Best Use (HBU) definition. Ambiguity and complexity of the HBU definition increase the difficulty to achieve the ultimate target: legally permissible, physically possible, and financially feasible, especially for mixed-use developments. This vagueness in HBU valuation may causes uncertainty for decision making and requires a set of more flexible strategies. This research aims to trace the sources of this ambiguity and examine the possible implications.