Two assessments of readiness for supplementary immunization activities (SIA) by independent partners led to timely corrective action and helped to improve readiness from 33 percent to 79 percent between the two assessments. This experience will help improve preparedness and ensure high-quality SIAs in the countries in the WHO South-East Asia Region as the region prepares to vaccinate >500 million children with measles-rubella vaccine through SIAs by 2019. India adopted the goal of measles elimination and rubella and congenital rubella syndrome (CRS) control by 2020. Achieving this goal requires SIAs using measles-rubella (MR) vaccine. Nationwide MR SIAs for children ages 9 months–14 years began in 2017and are to be completed by first quarter of 2019. SIAs require substantial preparation. To ensure high-quality SIAs, researchers performed an SIA readiness assessment. This report describes the process and experience of implementing SIA readiness assessments in three Indian states (Andhra Pradesh, Kerala, and Telangana).