Local authorities are engaged in numerous actions in favor of the environment. The City of Paris is interested in new tools to take into account environmental impacts of their urban planning projects during the different stages of the project design. Life Cycle Assessment (LCA) tools allow environmental impacts of a building to be evaluated during its life: construction, exploitation, end of life. In this article, we test an LCA tool on an urban planning project in Paris (France) in order to analyze the relevance of LCA for assessing district impacts and being a decision support tool.