Urban Planning has an immense impact on local microclimate which in turn affects the comfort and creating the urban climate. space quality within a city. The urban open spaces play an important role in view factor (SVF) and the The urban streets vary in geometry as defined by height/width ratio, sky orientation that is defined by its long axis. This directly influences the absorption and emission of incoming solar and outgoing long wave radiation which has a significant impact on the temperature variations within the street as well as the surrounding environment (Urban Heat Island). The objective of this research is to evaluate and to compare how the microclimate variation of urban street canyon can affect the built environment. Therefore the main aim of this paper is to discuss and assess the impact of the geometry on the street climate, in down town of Constantine-Algeria (semi and climate). In order to achieve this goal, a series of site measurements, are utilised. The preliminary results strongly indicate an air temperature difference of about 3-6 degrees C between the urban street and its surrounding rural environment. (C) 2009 Elsevier Ltd. All rights reserved.