Abstract: In this study the applicability of a night-time Operational Linescan System (OLS) sensor in urban population estimation has been examined. The study area consisted of the Indian portion of the Indo-Gangetic Plains. Using night-time OLS data, urban areas situated in the study area were mapped and their areal extent was determined. A linear relationship between the natural log of the urban area and the natural log of the corresponding population was established. The model was calibrated for the year 2001 and then validated for the year 1995. Subsequently, the model was modified using ancillary factors such as electricity consumption to reduce the error in population estimation. Thus, this study attempted to explore the applicability of nighttime OLS data in urban population estimation.