For efficient water resources planning and management, estimation of runoff in a catchment is of utmost importance. Geographic information systems (GIS) offer many new opportunities for hydrological modelling. It can be used to collect, handle and processing of both spatial and non-spatial data required for hydrological modelling. In the present investigation remote sensing and GIS techniques have been used for the rainfall runoff modelling of an urbanized sub-watershed (Anasagar) of Ajmer city (India). Rainfall runoff modelling has been carried out using EPA SWMM model for three years i.e. 1997, 2000 and 2002. EPA SWMM model is a physically based distributed model having capabilities of continuous as well as event based simulation. Land use/cover information has been obtained from remotely sensed images. Maximum Likelihood Classifier (MLC) has been used for the classification of remote sensing images of year 1997, 2000 and 2002. SWMM model parameters were extracted from the GIS database to estimate the runoff responses for the Anasagar sub-watershed. First of all conceptual runoff model was created using the data obtained from GIS database. Green Ampt’s model has been used for the estimation of infiltration. Overland flow routing has been done using Manning’s non-linear flow routing equation for the overland flow routing. Kinematic wave model has been used for flow routing in the channels. Continuous simulation was carried out for whole monsoon season (June to September) using three hourly rainfall data. Further, the model was calibrated using the observed data of the Anasagar Lake. Model parameters selected for the calibration includes depression storage, width of overland flow, and Manning’s coefficients for the overland flow routing. The study has provided the calibrated parameters of a typical urbanized sub-watershed, which have not been reported so far. Such studies are helpful in impact assessment of urbanisation on hydro-geological characteristics of watersheds and for the optimum planning and development of water resources.