The main material of wooden structures is wood, can be obtained easily in nature and higher strength per unit weight as well as eco-friendly and process of the manufacture has been superb. A weak point is Knots, while, cross grain, vermin by insects, fire and strength degradation due to fatigue and corrosion by deterioration. especially the deterioration of the wooden structure must be accompanied by appropriate conservation measures, because it is most the cultural assets. Conservation of wooden structure as possible, reuse the original repair itself, the consideration of the cultural value of attending to the basic principle is to maintain a archetype. Accordingly, the physical and chemical combined methods using a synthetic resins is emerging. A study on conservation methods using synthetic resins is only a short time. So former studies was the aspect of pure science to conserve, it is not that improvement of capacity using synthetic resins in wooden structures. The purpose of this paper is about flexural capacity of circular section wood using synthetic resins, the 11 specimens are manufactured and made an experiment about reinforcement length, ratio, material strength, direction of synthetic resins as variable. The results of this paper has shown that flexural reinforcement of wood by synthetic resins are efficient and found the possibility of using.