Under a given tradable credit scheme, travelers’ loss aversion behavior for credit charging during the route choice process is studied. A disutility function of loss aversion is applied to approach travelers’ different attitudes towards credit loss and gain, and the transaction costs of buying and selling credits are also incorporated in the function. The user equilibrium (UE) and market equilibrium (ME) conditions considering loss aversion effects are formulated into a variational inequality (VI) problem. Analyses demonstrate that the system optimum (SO) credit scheme does not always exist. A proposition is further presented to guarantee its existence.