Measurements of single-molecule chemical reaction kinetics are demonstrated for interfacial electron transfer from excited cresyl violet molecules to the conduction band of indium tin oxide (ITO) or energetically accessible surface electronic states under ambient conditions by using a far-field fluorescence microscope. In this system, each single molecule exhibits a single-exponential electron transfer kinetics. A wide distribution of site-specific electron transfer rates is observed for many single cresyl violet molecules examined. This work reveals that the physical origin of multiexponential kinetics of electron transfer in this system is the inhomogeneity of molecular-interactions on the semiconductor surface of ITO. We illustrate that the single molecule experiments provide detailed information not obtainable from experiments conducted on large ensembles of molecules. Single-molecule kinetics is particularly useful in understanding multiexponential behavior of chemical reactions in heterogeneous systems.