Korean building code requirements provide that the yield strength of longitudinal reinforcement shall not exceed 550 MPa in flexural members. The purpose of this paper is to evaluate the possibility of yield strength increase up to 600 MPa or 700 MPa in flexural reinforcement. Total 8 simple beam specimens divided by 3 groups tested for evaluating the flexural performance. Main test variables were yield strength of longitudinal reinforcement, reinforcement ratio and cover thickness. Test data analyzed in the viewpoint of cracking load, ultimate flexural strength, load-deflection relationship, crack progress, failure aspects and ductility. Test results indicate that flexural capacity of the specimen is similar from a standpoint of unit strength-area of reinforcement, but ductility of the specimens with high strength reinforcing bars was reduced in high reinforcement ratio. Flexural stiffness of the specimens with high strength reinforcing bars was also reduced, and this phenomenon is well agreed with the reduction of effective moment of inertia $I_e$. This paper concluded that flexural strength can be calculated using the present code provision without any change, but deflection checkup will be needed when the flexural member design with high strength reinforcing bars.