Muons have been accelerated by using a radio-frequency accelerator for the first time. Negative muonium atoms (Mu−), which are bound states of positive muons (μ+) and two electrons, are generated fromμ+’s through the electron capture process in an aluminum degrader. The generatedMu−’s are initially electrostatically accelerated and injected into a radio-frequency quadrupole linac (RFQ). In the RFQ, theMu−’s are accelerated to 89 keV. The acceleratedMu−’s are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.