The ACI 318-08 Code requires the maximum amount of shear reinforcement in reinforced concrete (RC) beams to prevent possible sudden shear failure due to over reinforcement. The design equations of the maximum amount of shear reinforcement provided by the current four design codes—ACI 318-08, CSA-04, EC2-02, and AIJ-99, differ substantially from one another. ACI 318-08, CSA-04, and EC2-02 provide an expression for the maximum amount of the shear reinforcement ratio as a function of the concrete compressive strength, but AIJ-99 does not take into account the influence of the concrete compressive strength. For high-strength concrete, the maximum amount of shear reinforcement calculated by EC2-02 and CSA-04 is much greater than that calculated by ACI 318-08. This paper presents the effects of shear reinforcement ratio and compressive strength of concrete on the maximum shear reinforcement in RC beams. Eighteen RC beams that have various shear reinforcement ratios were tested. Although designed to have considerably more shear reinforcement than that required in ACI 318-08, the test beams failed in shear after the yielding of shear reinforcement.