Reactive powder concrete (RPC) is a new type of ultra high-strength and high ductility concrete first developed in the 1990’s in France. It is recognized as a revolutionary material that provides a combination of ductility, durability, and high strength. In this paper, the RPC mixture proportioning is optimized and its mechanical properties, such as compressive strength, flexural strength, elastic modulus, and its durability are tested and discussed. Based on the optimal mixture proportion, eight simply supported RPC beams are made and tested. The mechanical properties of RPC beams, including section deformation, load-displacement relationship, failure forms, crack distribution, crack extension, and ultimate flexural capacity, are discussed. It is concluded that RPC is an excellent material with high strength and durability. The section deformation of RPC beams is accordance with the assumption of a plane cross-section. Steel fiber is important to control the crack extension and to improve the ductility of RPC beams. For RPC beams without reinforcement, only one main crack occurred during the failure process, and for RPC beams with reinforcement there were many subordinate cracks created near the main cracks. If the amount of reinforcement is increased, the number of subordinate cracks will increase.