Growing e-waste and the dwindling of nonrenewable materials underscore the urgency to develop electronics based on renewable natural resources. Using cellulose as a material for 3D printing living fungal electrodes is a novel way to harness their metabolic activity for potential use in electrochemical devices. This study shows that the yeast Saccharomyces cerevisiae and the white-rot fungus Trametes pubescens in combination with cellulose nanocrystals and cellulose nanofibrils can be 3D-printed and that both fungi grow inside the inks. Adding carbon black and graphite flakes to the inks makes them electronically conductive for potential use as electrodes in fungal batteries, specifically microbial fuel cells (MFCs). A single battery produces a maximum power density of 12.5 μW/cm² and a maximum current density of 49.2 μA/cm² (22 kΩ). These fungal biobatteries can produce between 300 and 600 mV for several days, delivering 3-20 μA for external loads between 10 and 100 kΩ. Attaching four batteries in parallel can power a small sensor for 65 h. Also, a fully biodegradable fungal MFC can be constructed with beeswax and a customized cellulose proton exchange membrane. This is the first study that reports on 3D-printed cellulose-based fungal electrodes in an MFC.