A process for producing prussic acid by subjecting methanol to a gas-phase contact reaction with molecular oxygen and ammonia in the presence of a catalyst, wherein said catalyst is an oxide composition containing iron, antimony, phosphorus and vanadium with a content of vanadium content being at least 0.6 in terms of atomic ratio relative to iron content taken as 10, and a mixed raw material gas for the gas-phase contact reaction contains oxygen at an oxygen-to-methanol molar ratio of less than 1.6.