With the arrival of composite materials, because of their unique properties, the ideas were presented in order to strengthen and improve their performance. The ideas were causing building of Grid composite structures. These structures have most widely used in the aerospace, missile and Marine industry because have made ideal mechanical properties: special stiffness and high strength against impact and fatigue. Grid composite plates are made from thin composite shell connected by series composite ribs. Ribs network results in a significant increase in stiffness and strength of structure. In this research, experimental and numerical investigations of effect of Shape of ribs have been on flexural behavior of grid composite plates. For this purpose, three types of Grid plates were considered with triangle, square and rhombic ribs. For the building these plates, silicone mold was designed and built and also was used for making plates from hand lay-up and hand-wound layer technique. Samples were subjected to three-point bending test that for this purpose, the fixture was designed and built. From numerical solution of the problem and compared with experimental results was observed that there is very little difference between experimental and numerical results. Experimental results show that special flexural stiffness of plate with square rib is 1.92 and 1.88 plate with triangular and rhombic ribs, respectively. Also, the flexural strength of plate with square rib is 1.58 plate with triangular rib. Thus plate with square rib is the highest stiffness and bending strength Keywords