Acoustic wave devices utilizing plate waves in thin lithium tantalate (LiTaO₃) have the potential of achieving high resonance frequency with a suitable electromechanical coupling factor and a relatively small temperature coefficient of frequency (TCF). The influence of Euler angle and plate thickness on the characteristics of plate waves has been investigated. High-frequency resonators using first antisymmetric Lamb wave mode (A₁) in (0°, 42°, 0°) LiTaO₃ thin plates have been fabricated and optimized. The resonance frequency is as high as 5 GHz, with a relative bandwidth of 7.3% and an impedance ratio of 72 dB. Finally, the TCF of (0°, 42°, 0°) LiTaO₃ has been evaluated. Therefore, it is proved that A₁ Lamb wave mode propagating in LiTaO₃ at a Euler angle close to (0°, 42°, 0°) is suitable for high-frequency devices.