Over the coming decades, many locatons are predicted to see warmer temperatures and more frequent extreme heat events as a result of climate change. Rising temperatures, coupled with the urban heat island effect, are expected to exacerbate existng conditons in cites. As a consequence, heat mitgaton in urban areas is antcipated be one of the key challenges of the twenty-first century. A frequently advocated means of mitgatng the urban heat island is through shade trees. Through the reducton of air and radiatve temperatures, they also improve the outdoor human thermal comfort and reduce building cooling loads. Utlizing four Hungarian metropolitan block typologies as cases, a numerical simulaton study is carried out to assess the impact of shade trees on the microclimate within urban blocks. The study applied ENVI-met for microclimate simulaton and MATLAB for the analysis and visualizaton of the results. Microclimate conditons within the blocks---with and without trees---are examined on the basis of diurnal air and mean radiant temperatures. Findings indicate that microclimate improvement by way of trees are primarily achieved through shading. The greatest reducton in daytme air and radiatve temperatures is achieved in configuratons with large open spaces, suggestng that effectve heat mitgaton strategies should also consider the interference between the shading of trees and buildings.