Résumé : It has been widely recognized that the microfinance sector should pursue both social and financial objectives (double bottom line objective). However, with the growing success of microfinance, numerous microfinance institutions (MFIs) experience mission drift when they focus only on their financial mission at the expense of their social one. The mainstream incentive schemes set up by MFIs for their loan officers are one of the factors contributing to mission drift for several reasons. First, monetary rewards based on financial criteria may lead unscrupulous loan officers to push clients into overindebtedness. Second, financial incentives may have a negative effect on the prosocial motivation animating numerous microfinance loan officers. In this paper, we attempt to suggest, with a mathematical model, an optimal incentive scheme double bottom line on which MFIs could rely in order to preserve loan officers’ prosocial motivation while paying attention to their financial profit.