Polymer concrete possesses viscoelastic properties conditioned by relaxation processes in the polymer binder. Their acceleration with an increase of temperature (principle of time-temperature equivalence) is used in predicting the long-term creep of polymer concrete. Physical aging of the polymer binder influences the creep of polymer concrete. To predict the long-term creep accounting for the aging process, an attempt to improve the time-temperature equivalence principle was undertaken. As a result of the experimental study of polyester resin-based concrete and its structural components (a resin unfilled and filled with diabase flour), it has been established that the changes in the creep compliance of the material follow according to the principle of the time-aging time equivalence with the reduction function depending on aging temperature. To predict the long-term creep of polymer concrete, a function of the time-temperature-aging time reduction was applied.