In this article we study the asymptotic behavior of solutions, in the sense of pullback attractors, of the evolution system utt + ∆ 2 u + a(t)∆θ = f (t, u), t > τ, x ∈ Ω, θt − κ∆θ − a(t)∆ut = 0, t > τ, x ∈ Ω, subject to boundary conditions u = ∆u = θ = 0, t > τ, x ∈ ∂Ω, where Ω is a bounded domain in R N with N ≥ 2, which boundary ∂Ω is assumed to be a C 4-hypersurface, κ > 0 is constant, a is an Hölder continuous function and f is a dissipative nonlinearity locally Lipschitz in the second variable. Using the theory of uniform sectorial operators, in the sense of P. Sobolevskiȋ ([23]), we give a partial description of the fractional power spaces scale for the thermoelastic plate operator and we show the local and global wellposedness of this non-autonomous problem. Furthermore we prove existence and uniform boundedness of pullback attractors.