A successful urban planning and design solution ought to present a comfortable setting for its pedestrians inside urban canyons, because it is fundamental to encourage a good quality urban life and promote health and wellbeing of humans. Recent findings have demonstrated that microclimate inside urban canyons has substantial influence upon the outdoor thermal comfort at the street level .This study, therefore, intends to devise early stage building and urban design strategies to improve outdoor thermal comfort. For this study, a number of existing urban canyons in Dhaka city have been chosen with a range of geometries combined with a variety of street orientations. The microclimatic characteristics of the canyons are analysed through a high resolution CFD microclimatic model: ENVI-met Version 4. Thermal comfort was evaluated with the PET index with the aid of RayMan1.2. Important findings include that deeper street canyons result in reduced air temperature but increased Tmrt thus presenting apparently conflicting design options to achieve outdoor comfort. However, such apparently conflicting findings offer the potential for designers to find a variety of canyon geometries appropriate for a tropical city context.