The present invention provides a pH stabilizing heat transfer medium composition comprising a main component of water, glycol, alcohol or glycol ether, and a pH buffer agent. The pH buffer agent is comprised of an alicyclic compound where a single ring-constituting carbon atom is bonded to two identical members or two different members selected from the group consisting of carboxymethyl and its salts, or where at least two ring-constituting neighboring carbon atoms are each bonded to a single member selected from the group consisting of carboxymethyl and its salts.