Timber is one of the materials widely used in construction and industry all over the world. In this paper, the behavior of strengthened timber beams made of beech wood (Fagus orientalis) were investigated experimentally. The composite timber beams were reinforced with flat, U-shaped, and L-shaped pultruded Glass Fiber Reinforced Polymer (GFRP) profiles. The GFRPs were attached to tensile or both tensile and compressive surfaces of beams. Altogether, 24 specimens, including 20 strengthened beams and 4 un-strengthened (control) beams, were tested under three-point bending test. Flexural behavior of specimens was evaluated through their load versus mid-span displacement curves, ultimate load carrying capacity, stiffness, displacement ductility, and capacity of energy absorption. The experimental results indicated that the mean value of modulus of rupture, flexural rigidity, ductility, and energy absorption of strengthened beams increased by up to 61, 59, 79, and 209% in comparison to control specimens, respectively. Finally, an analytical calculation has been conducted in order to predict the test data. There was a reasonable agreement between the test results and the results of numerical model.