A potentially implantable biocathode with the function of charge accumulation based on a nanobiocomposite including multiwall carbon nanotubes, polyaniline, and bilirubin oxidase is developed. The regularities of the functioning of the obtained electrode are studied in air-​satd. phosphate buffer soln., pH 7.4 (PB)​, and also in phosphate buffer soln. contg. redox-​active blood components (BMB)​. The open circuit potential of the biocathode is 0.33 and 0.08 V vs. the SCE in PB and BMB, resp.; it is completely restored after at least three self-​charge​/discharge cycles with connection to resistors with different resistance. Bioelectrocatalytic c.d. of oxygen redn. is 0.50 and 0.42 mA cm-​2 with the residual activity of 78 and 60​% of the initial value after 12 h of continuous operation in PB at 25°C and in BMB at 37°C, resp.