Surface chemical reactivity is imaged by combining electrochemical activation of a surface transformation process with spatiotemporal ellipsometric microscopy. An imaging ellipsometric microscope is built, allowing ellipsometric images of surfaces with a lateral resolution of ∼1 μm and a thickness sensitivity of ∼0.1 nm in air and 0.4 nm in a liquid. These performances are particularly adapted for using such optical setup as an in situ, real time chemical microscope to observe a chemical surface transformation. This microscope is tested for the monitoring of the electrochemically actuated diazonium grafting of a gold surface. Such reaction is a model system of organic material deposition on a gold surface induced by an electrochemical actuation. Using either plain or physically or chemically structured electrodes, it allows for the characterization of local phenomena associated with the electrografting process. This illustrates its potential to reveal the local (electro)chemical reactivity of surfaces.