This paper reports the low velocity impact behavior of preloaded E-glass/polypropylene sandwich composite plates. In particular, the effects of the type of preload and pre-strain amount on the impact behavior of composite plates are reported. Low velocity impact tests of specimens subjected to biaxial tension, compression and tension-compression (shear) were carried out using a drop-weight impact machine under a hemispherical impactor. Deformations ranging from 250 to 500 microstrains were imposed by a special fixture fabricated for this purpose. Single impact loadings were applied to the composite sandwich structures at different impact energies which were varied from rebounding case (10 J) to the perforation case (40 J). Impact results were explained in terms of typical contact force – deformation (F-D) curves and energy – time diagrams. The maximum contact force, deformation and absorbed energy of the specimens were compared to investigate the influence of pre-strain amount. In addition to the single impact tests, repeated impact behavior of composite sandwich structures subjected to different preload types were obtained with the same impact energy levels. The experimental results showed that the maximum contact force and maximum absorbed energy were considerably different in these situations. However, the repetition number of the specimens at the higher impact energies subjected to shear preloads was largely unaffected.