This study aims to examine the time-varying effects of greenbelt cancellation on surrounding land values, using random-coefficient multilevel modeling. The study site is Wirye New Town in Seoul, South Korea, an example of a government-driven urban development project on a repealed greenbelt, and the study period is from 1996 to 2015. The results suggest that the greenbelt cancellation has generated positive externalities on the remaining nearby greenbelt within a 500-m range, peaking at the groundbreaking for construction of the project, up to a price increment of 11.2% for each 100 m closer to the site. For non-greenbelt land parcels, a similar pattern was observed: externalities peaked at the announcement of the development plan with a relatively lower magnitude—up to 2.1%. These positive externalities might be due to increased expectation for a continued cancellation of greenbelts and heightened investment potential. In the rest of the study site beyond the 500-m range, the greenbelt cancellation and subsequent urban development seemingly yielded negative effects on both the greenbelt and non-greenbelt land parcels. Or, alternatively, the greenbelt effects might possibly be negligible due to remoteness, being masked by the effects of proximity to the urban center. The findings of this study will provide urban planners with better understanding of the economic impact of greenbelt cancellation on land markets.