Purpose The operations and viability of microfinance institutions (MFIs), crucial for socioeconomic development and poverty reduction, heavily rely on the multilevel relationships among borrowers, loan officers and MFIs. This study examines the relationship between interpersonal and firm-level relationship quality (RQ) and their simultaneous impact on customer loyalty (CL) in microfinance. Additionally, it investigates the mediating effect of firm-level RQ between CL and interpersonal RQ.Design/methodology/approach In this study, correlational research methods were employed. Completed questionnaires were received from 498 MFI borrowers in Dar es Salaam and Mwanza cities. Regression techniques and structural equation modeling were utilized to analyze the data. Before hypothesis testing, the validity and reliability of the measurements were confirmed.Findings Interpersonal-level and firm-level RQs are significantly related. Interpersonal-level RQ and its dimensions are significantly linked to CL, whereas firm-level RQ and its dimensions are insignificantly related to CL, except for commitment. Interpersonal-level relationships have a stronger impact on CL than firm-level relationships. Among all the dimensions of RQ, commitment has the greatest influence on CL at both levels. Firm-level RQ negatively and insignificantly mediates the relation between interpersonal-level RQ and CL.Research limitations/implicationsThe study findings only apply to Tanzania's microfinance industry, because the interactions between and the relative effects of firm and interpersonal ties may vary across various contexts and cultures. Future research may consider replicating this study in other contexts and cultures to confirm these findings.Practical implications This study advances the understanding of how multilevel relationships affect CL within the microfinance industry. This insight will assist MFIs and policymakers in identifying alternative and more efficient relational strategies to enhance CL, a critical element for the sustainability of MFIs. In turn, the sustainability of MFIs in low-income countries like Tanzania holds paramount importance for stimulating socioeconomic development and, hence, achieving the goal of poverty eradication.Originality/value While previous studies on multilevel relationships concentrated on a single relational dimension (trust) and were conducted within the realms of retail, airline and industrial manufacturing, the current study employs the three most popular relational dimensions: trust, commitment and satisfaction, within the microfinance context. Additionally, this study investigates the mediation effect of firm-level RQ between interpersonal-level RQ and CL, a previously unexplored area in research.