Hawking's black hole area theorem can be tested by monitoring the evolution of a single black hole over time. Using current imaging observations of two supermassive black holes M87* and Sgr A* from the Event Horizon Telescope (EHT), we find their horizon area variation fractions are consistent with the prediction of the black hole area law at the
confidence level. We
point out that whether the black hole area law is valid or not could be
determined by future high precision EHT observations of Sgr A*.