The extent to which microfinance bank institutions have contributed to the financial sector growth has not been well unraveled in the extant literature in Nigeria, hence, this study examined the effects of microfinance banks on financial sector growth in Nigeria. It further investigated the dynamic form of relationship between microfinance banks and financial sector growth in Nigeria covering a temporal scope 1992 to 2018. The model specification was formulated using financial sector GDP as the proxy for dependent variable, microfinance credit, deposits, assets and investment were used as proxies for microfinance banks institutions. Secondary data were sourced from CBN statistical Bulletin and analyzed using auto regressive distributed lag bound test and its corresponding short and long run coefficients. Finding revealed an inconclusive long run relationship between microfinance bank institutions and financial sector growth. Checking the individual variable coefficients in the short run, microfinance credit has significant positive effect while microfinance assets has insignificant effects on financial sector growth. In the long run, it was revealed that microfinance bank deposits and assets exert insignificant positive effects while microfinance credits have insignificant effect and investments have significant negative effects on financial sector growth. The study concluded that, in the long run, microfinance bank institutions exert positive and insignificant effects on financial sector growth in Nigeria. It was therefore recommended that, for microfinance bank institutions to impact significantly on financial sector growth in Nigeria, its credit should be increased and be more directed to the target individuals and the level of their investments should be geared up so as to engender growth of the financial sector in Nigeria. Furthermore, microfinance bank institutions should maintain its status quo on deposits and assets, however, improvement on them should be encouraged so as to enhance the growth of the financial sector in Nigeria