The uniaxial tensile tests of Reinforced Concrete elements with Carbon fiber sheet (RCC) are conducted to clarify the basic mechanical characteristics which affect the tension stiffness of RCC. This paper mainly presents the difference between RCC and ordinary Reinforced Concrete member (RC) in the load carrying capacity, the average crack spacing, stress and/or strain distributions of steel, and the average stress - strain relationship of concrete. Crack spacing of RCC becomes smaller between 25% and 60% of that in RC as the amount of Carbon Fiber Sheet (CFS) increases. The strain distributions of steel in RCC before and after the yielding of steel differ from those in RC. The tension stiffness developed by the bond action of CFS increases as the amount of CFS increases but that of steel becomes less. With the steel and CFS contributions combined, the tension stiffness of concrete as a whole generally becomes greater than that in RC. There is, however, a case in which tension stiffness of concrete in RCC decreases more than that in RC, because the average bond stress of steel rapidly decreases after the yielding of steel.