Inorganic graphene analogues (IGAs) are promising catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their catalytic activities need to be improved. Herein, we report atomically thin SiC obtained via a simple ultrasonic treatment of commercial SiC as an efficient electrocatalyst for the ORR in alkaline and acidic media. Due to the advantages of its unique surface composition and structure, the atomically thin SiC shows remarkable catalytic activity for the ORR and the number of electrons transferred per O₂ is close to four in both alkaline and acidic media. Compared with commercial Pt/C, the atomically thin SiC possesses prominent durability and tolerance to methanol crossover, and thus can be developed into a low-cost and efficient alternative as a cathodic electrode in fuel cells.