This paper presents the transient response analysis conducted for sandwich plates subjected to blast load. These plates are made of two isotropic face sheets and a porous core composed of closed-cell foam. The core with functionally graded pore distribution through the thickness direction is uniformly reinforced using graphene nanoplatelets. Three different porosity distributions are considered, namely, two functionally graded symmetric types and a uniform type. In the analytical method of investigating the transient response of sandwich plates, Reddy’s third order shear deformation theory is employed. To verify the reliability of the presented analytical method, the transient responses are compared to those obtained using the ANSYS software. The influences of the weight fraction, geometry of the graphene nanoplatelet, porosity distribution and porosity coefficient on the transient response are examined using a few examples.