Abstarct: The mechanical behavior of composite lattice sandwich plates, as key components in engineering structures, holds significant importance. The addition of reinforcing strips in various configurations and at different orientations on the inner surfaces of these plates has a negligible effect on the overall weight of the structure while substantially enhancing its load-bearing capacity. In addition to homogeneous reinforcing strips, including reinforcements, particularly unidirectional fiber-reinforced composite reinforcements aligned with the strips, significantly improves the structural strength against axial, shear, and bending loads. This study investigates the linear and nonlinear free and forced vibration behavior of rectangular sandwich plates with a composite lattice core, which feature different geometric patterns and are made of homogeneous orthotropic materials. The analysis is conducted using an analytical approach baxsed on the first-order shear deformation theory. First, the equations of motion are derived using Hamilton’s principle. Then, the multiple-scale method is employed to determine the primary and secondary resonances of single-mode rectangular sandwich plates. Finally, the effects of key system parameters, such as thickness, height, and different reinforcement angles, on the linear and nonlinear frequencies are thoroughly analyzed. To validate the accuracy of the proposed solution method, the results are compared with available data from the literature, the finite element method, and the fourth-order Runge-Kutta numerical method. This comparison demonstrates a high degree of agreement with the frequency response of the model, confirming the validity of the presented dynamic analysis. The findings reveal that the geometry and configuration of the core’s reinforcing strips significantly influence the natural frequencies of the plate.