The computational effort to analyze a sandwich panel can be greatly reduced if an equivalent 2D thick-plate bending model is used instead of a detailed 3D finite-element model. The success of the transformation from a sandwich panel to a 2D thick-plate bending model depends on the equivalent elastic constants used. In this note, these elastic constants for Z-core sandwich panels are summarized. The elastic constant for the shear stiffness in the weaker direction for Z-core sandwich panels is derived. To ascertain the validity of the elastic constants, the results obtained from the 2D thick-plate bending model with different boundary conditions are compared with a detailed 3D finite-element model. From the results, it is shown that excellent agreement is obtained between the two models.