The influence of geogrid on the thermal expansion of reactive powder concrete (RPC) was experimentally investigated. Eighteen RPC prisms of dimensions 75×75×280 mm were tested at a temperature of 27±4°C and a relative humidity of 50±10% for 103 days. Triaxial geogrid having equilateral triangular openings with a side length of 35 mm was used as a reinforcement layer. The triaxial geogrid was placed at a depth of 37.5 mm from the surface of the RPC prism. Test results illustrate that the triaxial geogrid reinforcement significantly reduces the thermal expansion strains of RPC. In addition, the thermal expansion strains of RPC decrease with increasing the number of triaxial geogrid layers. The triaxial geogrid reinforcement could reduce the rate of thermal expansion of the RPC specimens compared with the unreinforced RPC specimens. An empirical equation was developed in this study for determining the thermal expansion strains of RPC reinforced with a single or a double triaxial geogrid layer.