Transition metal dichalcogenides (TMDs) have attracted a great deal of attention for potential applications in a variety of areas including integrated optoelectronic devices. Most of TMDs transform from indirect to direct band-gap semiconductors when their thickness is reduced to a monolayer. Therefore, monolayer TMDs could serve as efficient optical gain materials, especially for making nanolasers with the smallest possible volume of active medium. Such lasers with small gain media could be important as light sources for integrated photonics for future on-chip interconnects, where extreme low energy consumption is required. Furthermore, the large exciton binding energy in monolayer TMDs exceeding 0.5 eV makes them important as potential candidate for exciton lasers at room temperature. So far, lasers based on monolayer TMDs have been reported at cryogenic temperatures, employing a monolayer WSe2 coupled onto a GaP photonic-crystal cavity, or a monolayer WS2 with a Si3N4 micro-disk. One of the possible reasons for the low temperature operation is the low Q-cavity as a result of the choices of cavity materials and structures and the associated fabrication precision. Here, we demonstrate the first room-temperature operation of a nanolaser using a monolayer molybdenum ditelluride nanolaser combined with a silicon nanobeam cavity. Lasing operation at 1132 nm is supported by the exciton emission with a linewidth of 0.202 nm and a Q factor of 5605. The room temperature operation shows the feasibility of TMDs nanolaser towards practical application. In addition, the silicon nanobeam cavity would make such 2D-based lasers more attractive for silicon photonics integration.