[1] Rainfall is probably the most important parameter that is predicted by numerical weather prediction (NWP) models, though the skill of rainfall prediction is the poorest compared to other parameters e.g. temperature and humidity. In this study, the impact of rainfall assimilation on mesoscale model forecasts is evaluated during Indian summer monsoon 2011. The Weather Research and Forecasting (WRF) model and its four-dimensional variational data assimilation (4D-Var) system are used to assimilate the Tropical Rainfall Measuring Mission (TRMM) 3B42 and Japan Aerospace Exploration Agency (JAXA) Global Satellite Mapping of Precipitation (GSMaP) retrieved rainfall. A total of five experiments are performed daily with and without assimilation of rainfall data during the entire month of July 2011. Separate assimilation experiments are performed to assess the sensitivity of WRF model forecast with strict and less-strict quality control. Assimilation of rainfall improves the forecast of temperature, specific humidity and wind speed. Domain average improvement parameter of rainfall forecast is also improved over the Indian landmass when compared with NOAA Climate Prediction Center Morphing Technique (CMORPH) and Indian Meteorological Department gridded rainfall.