Composite sandwich constructions offer light weight and high bending stiffness advantages for aerospace and automotive applications among other structures. The use of a hollow truss core or z-fiber pin core is a new concept in sandwich composites, where the core is hollow and accessible, thereby providing space advantages for fuel cells and/or electronic assemblies besides from possessing high shear and axial stiffness. The z-fiber pins are oriented at predetermined geometry’s and penetrate into the laminated facesheets making-up the sandwich composite. In the reference (Palazatto et. al, 1997), the low velocity response of hollow truss core composites with z-fiber pins oriented at 10 degree and 20 degree angles with respect to the facesheets were investigated by us. The current paper presents the post-impact microstructure, ultrasonic and vibration based nondestructive evaluation (NDE) studies and compression-after-impact response accompanied by acoustic emission (AE) testing of these composites.