This study develops a linear buckling model for double-layered microplate system filled with an elastic medium between layers using the modified couple stress theory and a two-variable higher-order shear deformation theory. The governing differential equations of system buckling are derived from the Euler-Lagrange equation. By applying the Navier method, the synchronous and asynchronous buckling solutions are analytically solved for the case of both upper and lower plates being simply supported on four edges. The influence of each parameter on the buckling characteristics of the system is discussed by selective examples. Numerical results showed that the asynchronous buckling characteristics of the system depend on the material length scale parameter, aspect ratio and elastic medium moduli, while the synchronous buckling characteristics depend on the first two only; the asynchronous buckling critical load is noticeable greater than that of the synchronous buckling case; the Pasternak modulus has a more significant effect on the buckling characteristics of the system than the Winkler modulus.