Real time observation of chemical reactions of individual noble metal nanoparticles (MNPs) is fundamentally important to their controlled synthesis, chemical sensing and catalysis applications. Here, with a simple and high-throughput single-molecule darkfield spectral imaging technique, we demonstrate that the reaction-induced plasmonic resonance variations of multiple MNPs could be monitored in parallel. Oxidation kinetics of individual gold nanorods (AuNRs), either immobilized on a glass substrate or moving freely in homogeneous solution, was recorded successfully. Heterogeneous reaction pathways and intermediate states unobservable in ensemble UV-visible measurements were revealed. Interestingly, the oxidation rate of individual immobilized AuNRs was much slower than that of the bulk AuNR solution, which implies the existence of a novel self-catalysis mechanism. This high-throughput darkfield spectral imaging technique could be applied to chemical reaction kinetics and heterogeneous catalysis studies of other MNPs at single particle level.