This study aims to identify the impact of internal marketing (IM) on business performance (BP) in the banking sector in Bangladesh where employee relationship quality (ERQ) as a mediator as well as to determine the importance of each of the internal marketing dimensions in explaining the variation in internal service quality. Convenient sampling is used to choose respondents for this study where an online questionnaire survey was activated to collect data. Using a direct questionnaire survey carried out in the banking sector and the present study obtained 402 useable responses. A conceptual model was validated using the partial least square (PLS) method, a methodology based on structural equation model using the software Smart-PLS version. The study results revealed that internal marketing of banking business is positively correlated with business performance through relationship quality. The findings should not be enthusiastically widespread across the banking sectors in Bangladesh.