Mixed matrix membranes (MMMs) based on the polyimide Matrimid® (PI) with metal-organic framework (MOF) MIL-101(Cr) as porous nanostructured filler were synthesized and applied as separation element in a membrane reactor to carry out the esterification of acetic acid with ethanol. The MMMs were characterized by techniques including X-ray diffraction, IR spectroscopy and scanning electron microscopy. In order to compare the performance of MIL-101(Cr)-PI MMMs in the membrane reactor, pure PI and HKUST-1-PI membranes were also used. MMMs provided a better reactor performance than the bare PI membrane because of the increase in permeability associated to the presence of MOF as filler. The PI membrane reactor barely achieved the same conversion as a fixed bed reactor, while the MIL- 101(Cr)-PI membrane showed a reactor performance similar to that of the HKUST-1-PI membrane with higher stability, as confirmed by membrane characterization after the reaction experiments.