C45 steel has a wide range of industrial fields due it can be used in many mechanical parts. The conventional grinding wheels (continuous working surface) were used in finishing processes of C45 steel machine parts. However, these kinds of grinding wheels had some disadvantages due to high cutting force and high working temperature... that lead to very damaged on workpiece surface. The cutting efficiency of abrasive grains and the grindabilities of grinding wheels were reduced. In this paper, the grinding process of machining hardened C45 steel using newly developed grinding wheels and conventional grinding wheel was observed. Discontinued rate n is defined as a ratio between the discontinued regions and the circumference of the grinding wheel's working surface. There were five newly developed grinding wheels with different n (10.91 percent, 16.37 percent, 18.19 percent, 20.01 percent and 21.83 percent respectively) and one conventional grinding wheel, which has n of 0 percent were used to grind hardened C45 steel. The results showed that material removal rates, Vkl in a unit time of grinding wheel with n 16.37 percent was 13.2 percent higher than that of conventional grinding wheel.