An antifreeze/coolant composition is disclosed, which can effectively inhibit corrosion of metals, particularly cast aluminum and cast iron, and can also inhibit cavitation damage to metals in an engine cooling system. The antifreeze/coolant composition comprises a glycol as the chief ingredient, 0.1-0.5% by weight of at least one ingredient selected from among C.sub.6 -C.sub.12 aliphatic monobasic acids and their salts, and 0.1-0.5% by weight of at least one ingredient selected from among alkoxybenzoic acids having C.sub.1 -C.sub.5 alkoxy and their salts.