This paper aims to discuss one of the most troublesome issues of urban planning in Taiwan: Do a city's development, expansion, and construction necessarily contradict the preservation of historical environments and community cultures? Tracing the epistemological foundation of urban planning, this paper suggests that the ignorance of cultures and disadvantaged groups by Taiwan's planning institutions results from its over-simplified understanding of the concept of public interest. Next, this paper analyzes the relation between public sphere and public interest and develops the concept of multiple public interests as an analytical framework to examine the contradiction between historic preservation and urban planning. Third, looking at the preservation movement of Taiwan Provincial Leprosarium, I points out the multiple spatial imaginations of this site held by various social groups and how these imaginations include or exclude certain public interests. Finally, I suggest that radical planner should propose planning strategies that conforms to the principles of social justice, and face up to the emergence of new planning practices as well as new planning subjects.