Reliability of electricity supply is one of pressing challenges to many micro and small enterprises (MSEs) in developing countries. MSEs play a pivotal role in employment generation in these countries, but productivity of MSEs is relatively low. Little is known about how blackouts affect performance of MSEs. This paper is the first study to estimate the impact of power blackouts on productivity of manufacturing MSEs and to discuss the role of the government in addressing problem. We employ a pseudo-panel dataset covering six firm cohorts within 21 Indonesian national electricity company working areas from 2010 to 2015. Our identification strategy involves first examining blackouts determinants and then using these determinants as instruments in an IV dynamic panel fixed effects estimation while controlling for factors potentially affect productivity and correlated with blackouts. We find that electricity blackouts reduce the average labor productivity and the resultant loss amounts to approximately IDR 71.5 billion (USD 4.91 million) per year in Indonesia. Therefore, it is crucial to improve electricity supply reliability in developing countries. We find that introducing a captive generator as a way to cope with power outages, is positively associated with productivity, and MSEs that have captive generators benefit more when the power supply is poor. Our findings will assist policy makers to prioritize addressing power blackouts relative to other constraints MSEs face.