Electrospinning of uniform biohybrid fibers with concealed cellulose microfibrils (CMF) is reported as a promising and environmentally sound concept for reinforcement of polymer nonwoven fiber systems of fine dimensions. The extraction and refinement of the high-strength crystalline microfibril bundles (15−20 nm thick) from bacterial cellulose networks is presented, as well as their morphology prior to and post electrospinning, Nanofibers composed of a poly(methyl methacrylate) (PMMA) matrix with cellulose contents reaching 20 wt % were repeatedly obtained. A high degree of dispersion of the microfibrils was obtained for a variety of CMF contents and the aggregation of the CMF was greatly suppressed as the microfibrils were aligned and rapidly sealed inside the acrylate matrix during the continuous formation of the fibers. The limited CMF aggregation up to 7 wt % was related to a suppressed phase separation caused by the rapid solidification of the polymer solutions during spinning. The fibers’ diameters ...