In this experimental and numerical study, the effect of plate thickness, the diameter of circular cutout, the distance between circular cutouts and rowing orientation angle effect (${ heta}$) on the buckling load of E-glass/vinylester pultruded composite beams with single and double circular cutouts, were investigated. The composite beam having 2, 4, and 6 mm thicknesses was produced as [Mat/${ heta}$ /Mat/${ heta}$ /Mat] by using pultrusion technique. Seven different fiber angles as $0^{circ}$, $15^{circ}$, $30^{circ}$, $45^{circ}$, $60^{circ}$, $75^{circ}$, and $90^{circ}$ were chosen for investigation of rowing orientation angle. The distances between each circular cutout were selected as 15, 30, 45, 60, and 75 mm in the case of double circular cutouts. The diameters of circular cutouts were chosen as 2, 4, 6, 8, and 10 mm to investigate the effect of cutout size. The experimental buckling loads were compared with the results calculated from the numerical analysis. ANSYS 11 commercial software was used for numerical study. A good agreement was obtained between numerical and experimental results.