This paper is to investigate the impact of competition on the efficiency of the banking industry in Vietnam. Data are collected from the audited annual financial statements and the annual reports of 30 commercial banks during the period of 2010 – 2017. Lerner index is used to measure the market power of bank, while Data Envelope Analysis is employed to estimate the technical efficiency of bank. The impact of competition on the operational efficiency of commercial banks is estimated by Panel Vector Autoregressive model (PVAR). The empirical results seem to indicate that there is a positive impact of competition on the bank efficiency, which is in line with the “quiet-life” hypothesis. However, the statistical test does not confirm this at the traditional levels. Interestingly, the empirical results demonstrate a negative impact of bank efficiency on the market power of bank, and hence market competition. While this result shares the causality dimension with the “efficient structure” hypothesis, it presents an opposite sign on the causality. All these findings could be explained by the real situations and typical characteristics of the economy of Vietnam. This study has important implications for both researchers and practioners.