The structures of a sandwich composite have been utilized in the aerospace industry and engineering applications. Prediction of a theoretical composite construction's flexural properties is important for efficient composite products design. In this investigation, four different core shapes were used in the fabrication of the sandwich frames with constant volume of sandwich composite structure in each case; these are hexagonal, rectangular, triangular and circular. The effect of core stiffeners number was studied to finding the best stiffeners number which gives the highest properties in strength using the finite element analysis. The material of the each face sheet is consisting from epoxy with four layers of a woven fiberglass laminate construction, and the core stiffener material consists from epoxy matrix with carbon fiber, the fiber volume fraction was 60% for both skins and core composites.The analysis of the three point bending load with a value of (10 kN) conducted by constructing a finite element model, explained that the best shape of core was rectangular which give less deflection value of (11.939 mm) from the other shapes, for the same properties of material and constant core volume in each case. Also, it was determined the optimum stiffeners number, for the rectangular core, was five stiffeners in longitudinal direction and twelve stiffeners in transverse direction, gives strengthen structure.