This paper presents an experimental study on the flexural behavior of CFRP box beams with two laminate structures fabricated by VaRTM method. The two laminate structures are a cross-ply (CP) and a quasi-isotropic (QI). Three specimens are prepared for each laminate structure. The specimens are tested under four point bending. The bending tests show that initial stiffness of each specimen corresponds to the one calculated by Timoshenko’s beam theory and that the two laminate structures affect longitudinal normal strain and in-plane shear strain. QI exhibits higher flexural strength than CP, and they fail with different failure modes. Moreover, it is shown that the flexural strength calculated based on beam theory and Tsai-Wu criterion agrees relatively with the experimental one.