A way to prepare all-cellulose composites in a two-step extrusion process was investigated in this study. Cellulose fibers from regional plants miscanthus were first refined and chemical modified through reactive extrusion. In a second extrusion step, the modified cellulosic fibers were compounded with cellulose-based matrices to an all-cellulose injection-moldable composite. The mechanical properties of the composites were compared with their unmodified grades and with drop-in bio-PP und bio-PE matrices.