© 2015 Elsevier Ltd. Honeycomb as sandwich core construction has been established as one of the best candidates among ultralight cellular materials for load-bearing and energy absorption applications. In this paper, by introducing non-uniform mass distribution (gradient) in the core, substantially improved structural performance of a fully-clamped sandwich plate with square honeycomb core is achieved for out-of-plane uniform pressure loading. In-plane gradient of core is defined and achieved via two approaches: web thickness variation and cell size variation. Response of sandwich plates with linear in-plane core gradient is systematically investigated with finite element (FE) simulations. For both quasi-static and blast loading cases, it is found that positively graded cores exhibit advantage in stiffness, strength as well as plastic energy dissipation compared to cores without gradient or with negative gradient. Examination of plastic energy dissipation in a graded core reveals that ribs placed next to its symmetry plane are more sensitive to changes in thickness or location compared to those placed adjacent to the clamped edges. With the total mass of the core constrained, the constituent material can be more efficiently utilized by either increasing the thickness of ribs close to symmetry planes or moving ribs towards the symmetry planes.