ABSTRACT Importance of continuous monitoring of rainfall from Indian geostationary satellites INSAT-3D/3DR over India and surrounding oceans is not only necessary to monitor the performance of the monsoon, but is extremely useful in disaster mitigation support system as well. It has been observed that rain products from INSAT-3D/3DR often show overestimation in certain areas with unrealistic instances of intense rain, which need a closer examination. With this objective, the present study is carried out, which suggests that a non-linear calibration equation for thermal infrared brightness temperatures (Tb) of INSAT-3D/3DR is more appropriate than routinely applied linear equation for rainfall estimation. The study elaborates a new calibration correction method and addresses the requirement of such calibration. To evaluate the performance of proposed method, Hydro-Estimator (HE) operational rainfall products from INSAT-3D/3DR are re-estimated from the newly calibrated Tbs during Indian summer monsoon (June-September), 2020. The re-estimated HE rain not only substantially reduces the instances of overestimation, but also show remarkable improvement in capturing rainfall distribution over India and surrounding ocean. Improvement in RMSE from 8.56 mm/hr to 3.23 mm/hr, when compared with the concurrent IMERG (Integrated Multi-satellitE Retrieval for Global Precipitation Mission (GPM)) rain, shows reliability of the new method. Furthermore, the re-estimated HE rain compares better with in-situ rain gauges observations than the operational HE product with RMSE (bias) reduced from 85.43 mm/day (30.23 mm/day) to 40.02 mm/day (17.07 mm/day), and correlation improved from 0.28 to 0.32. The significance of the new calibration method is also recognized in the rain monitoring over complex hilly terrain and coastal regions of India.