Bond between a reinforcing steel bar and the surrounding concrete is made up of three components. There are chemical adhesion, friction, and mechanical interaction between the ribs of the bar and the surrounding concrete. Bond of deformed bars depends primarily on the bearing of the rib deformation against the surrounding concrete.Darwin(1996) performed an experinmental study of high relative rib area, bars, and Hammad(1995) tested of beam-end specimens and spliced beams, without confinement but there was a limited information.The effects of deformation properties on the bond of sreel reinforcing bars are studied to develop guildelines for commercially produced high relative rib area deformation patterns and accurate equations to predict bond strength. Interfacial bond mechanism between rib bars and concrete is also sudied to evaluation of effects of rib area on bond performance. This paper describes 2 kinds of experimnetal researches. 30 beam-end specimens are tested to investigate the effects of bar size and relative rib areas ranging from 0.104 to 0.162. And, 24 lap-splice beam specimens are tested to the same variables. Each test results are normalized and compared with the proposed equations of ACI 408 committee.The final objective of the study is to enhance structural stability, and workability thorough increasing the bond strength between deformed bar and surrounding concrete. The results of this study will be used to shorten bond and development length by 20~30 percent and it will facilitate to use of high strength and high-relative rib area bars.