The main objective of urban renewal is to improve neighborhood environment by reconstructing obsolescent buildings. There are three approaches for implementing urban renewal projects in Taiwan but developers prefer reconstruction to renovation and maintenance of buildings. Local government creates lots of criteria to define the qualified buildings which could be reconstructed. The basic criterion could be the life of buildings. Due to the renewal area should be involved continued lots; some new buildings could be planned into a renewal project. This might lead new buildings to be reconstructed when they are young. Constructing a building costs a lot and it should not be demolished just because of the reason of urban renewal. Therefore, in this paper, the building life of approved urban renewal units was examined for analyzing the efficiency of urban renewal projects in real estate market. The data of Construction Licenses, Usage Licenses and Demolition Licenses of the buildings involved in urban renewal projects were used for the analysis.