The effect of the difference in the thickness ratio of the double-layered thickness-shear resonator on the temperature characteristics of the resonance frequency was investigated using a Ca3TaGa3Si2O14 (CTGS) single crystal. Three specimens with thickness ratios of x = 0.25 , 0.33, and 0.50 were prepared using 122° Y - and 171° Y -cut CTGS substrates. For the specimens with x = 0.25 and 0.33, the temperature characteristics varied depending on the order of the resonance mode. For the specimen with x = 0.50 , on the other hand, almost the same temperature characteristics were observed regardless of the order of the resonance mode. To interpret this phenomenon, a new equation for predicting the temperature characteristics of the fundamental mode (first mode) for the double-layered resonator was created using the electric flux density ratio generated in the two substrates. The expected values using this equation were in good agreement with the result of the first mode temperature characteristics.