Abstract We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as a sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop, and is eventually reflected at the remote footpoint where significant brightenings are observed in all of the Atmospheric Imaging Assembly extreme-ultraviolet channels. This unique observation provides us with the opportunity to better understand not only the thermal properties and damping mechanisms of the sloshing oscillation but also the energy transfer at the remote footpoint. Based on differential emission measures analysis and the technique of coronal seismology, we find that (1) the calculated local sound speed is consistent with the observed propagation speed of the perturbation during the oscillation, which is suggestive of a slow magnetoacoustic wave; (2) thermal conduction is the major damping mechanism of the wave but an additional damping mechanism such as anomalous enhancement of compressive viscosity or wave leakage is also required to account for the rapid decay of the observed waves; (3) the wave produced a nanoflare at the remote footpoint, with a peak thermal energy of ∼10²⁴–10²⁵ erg. This work provides a consistent picture of the magnetoacoustic wave propagation and reflection in a coronal loop, and reports the first solid evidence of a wave-induced nanoflare. The results reveal new clues for further simulation studies and may help with solving the coronal heating problem.