Summary.Within the frame of the 3D-theory of thermo-viscoelastodynamics, a hierarchic system of 2D-equations is consistently derived in invariant differential and variational forms for the analysis of highfrequency motions of thin plates. First, a differential type of variational principles is presented in terms of the Laplace transformed field variables for the fundamental equations of linear, non-isothermal, nonpolar and non-local, 3D-theory. Next, a generalized version of Mindlin's hypothesis for elastic plates is introduced for the displacement and temperature fields. Then, the hierarchic system of plate equations is systematically established by means of the differential variational principle. The hierarchic system of 2D-equations governs the extensional, thickness-shear, fiexural and torsional as well as coupled motions of thermo-viscoelastic thin plates of uniform thickness at both low-and high-frequencies. Lastly, certain cases involving special geometry, motions and material are indicated. Also, the uniqueness is investigated in solutions of the hierarchic system of plate equations. fixed, right-handed system of curvilinear orthogonal coordinates time, time interval a finite and bounded regular region, its boundary surface and closure at time t thickness of plate, thickness interval midsurface of plate, Jordan's curve which bounds A components of the unit vectors normal to 0s2 (or A) and C components of the stress tensor components of the traction vector mass density components of the body force vector components of the displacement vector components of the linear strain tensor components of the alternating tensor components of the heat flux vector normal component of the heat flux vector across 0Y2 reference temperature, temperature increment from O0 entropy density components of the thermal field vector relaxation functions of the plate material components of the thermal conductivity tensor complementary subsurfaces of 0Y2 one-sided Laplace transform of X prescribed value of X and X of order (n)