Mergers of banks are planned and executed under strategic expertise to optimize the performance of entities and the success of these mergers is a matter of concern, not only for all market players, rather for the governments also, for economic development and targeting best utilization of resources. The State bank of India (SBI) is a multinational Indian public sector bank, operating in India, with major market share as well as total loans. The State banks group, comprising of SBI and its associates, in India has seen many mergers in the last decade, especially a grand merger in 2017, when five associates of state bank group, were merged in State Bank of India. This paper examines empirically, the impact of these mergers in terms of efficiency increase for SBI, using super efficiency data envelopment analysis (DEA), for a year wise relative efficiency evaluation, by analyzing the overall pre-merger and post-merger productivity, with a purpose to identify any significant rise in efficiency, in post-merger performance as compared to the pre-merger performance. This study endeavors to contribute to the existing literature by providing empirical research related to mergers. For the analysis, the present study uses the data for the variables owned funds, borrowings, deposits, wage bills, spread and other income for the SBI and its associates along with four other top performing public sector banks as per market capitalization at Bombay stock exchange, for the time period starting from 2015 through 2020. The findings reveal that the grand merger of 2017 resulted in a robust banking network of SBI, providing a stable position to the bank, on global level. Also, it sustained the weakly performing associates of the State bank group. [ABSTRACT FROM AUTHOR]