Furnace black СН600 was studied as a catalyst for electrosynthesis of Н2О2 from О2 in a gas diffusion electrode in alkaline and acidic solutions. The texture properties of the starting black СН600 and gas diffusion electrodes (GDEs) based on it were determined by the low-temperature nitrogen adsorption (LTNA) method. The rate constants of Н2О2 decomposition on black and its mixtures with fluoroplast-4D in acidic and alkaline solutions of electrolyte were calculated. The process selectivity γ (the current fraction spent on the two-electron reduction of oxygen), kinetic parameters of oxygen reduction, and double-layer capacity of the СН600-based GDE were determined. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis from oxygen in СН600-based GDE in acidic and alkaline solutions were obtained.