The main objective of this study is to assess the impact of gender on microfinance social efficiency. Our methodology is based on nonparametric techniques to estimate the gender effect. We use a conditional directional free disposal hull (FDH) approach as well as its robust version of order-; we study the effect of the heterogeneity factor on the difference of conditional and non conditional inefficiencies as well as on the inefficiency level using a local linear regression and we test the significance of its effect using a wild double bootstrap procedure. Using a cross-country sample of 680 microfinance institutes (MFIs) in 2011 from six main regions of the world, our findings suggest that gender diversity has globally a positive impact on the microfinance social efficiency. However, the nature of the effect depends on the considered heterogeneity factor and we find that the boardroom gender diversity effect is linear, whereas the effect of the percentage of women loan officers is non linear (U-shaped on the difference of inefficiencies and inverted U-shaped on the inefficiency levels). We assess the robustness of our findings on various subsamples (global or regional scale, and also depending on the considered profit oriented status). Our findings reinforce the importance of the role played by women in MFI social efficiency.