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 deuce 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 decreased significantly from similar to 1.8 mu m (1 wt %) to similar to 100 nm (20 wt %) with increasing cellulose contents, resulting in CMF agglomerations and percolating architectures within the acrylate host, which was consistent with microscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) evaluations. The nominal content of cellulose in the fibers was assessed by Lorentzian profile fit assignment of the crystalline vs amorphous fractions of the fibers' X-ray diffractograms. TGA of fibers with low CMF content revealed that both CMF and PMMA showed a significantly improved thermal stability in the composite material. The biohybrid fibers were continuously aligned into an anisotropic nanocomposite yarns from a liquid support during spinning. The strategy described herein may allow for new mechanically robust nonwoven fiber systems, or be used as implemented on existing electrospun formulations that are lacking mechanical integrity. It is envisioned that the cellulose microfibrils may be of importance in biomedical applications where biocompatibility is a requirement.