Various studies about harvesting energy for future energy production have been conducted. In particular, replacing batteries in implantable medical devices with electrical harvesting is a great challenge. Here, we have improved the electrical harvesting performance of twisted carbon nanotube yarn, which was previously reported to be an electrical energy harvester, by biscrolling positively charged ferritin protein in a biofluid environment. The harvester electrodes are made by biscrolling ferritin (40 wt%) in carbon nanotube yarn and twisting it into a coiled structure, which provides stretchability. The coiled ferritin/carbon nanotube yarn generated a 2.8-fold higher peak-to-peak open circuit voltage (OCV) and a 1.5-fold higher peak power than that generated by bare carbon nanotube yarn in phosphate-buffered saline (PBS) buffer. The improved performance is the result of the increased capacitance change and the shifting of the potential of zero charges that are induced by the electrochemically capacitive, positively charged ferritin. As a result, we confirm that the electrical performance of the carbon nanotube harvester can be improved using biomaterials. This carbon nanotube yarn harvester, which contains protein, has the potential to replace batteries in implantable devices.