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 $1{\textstyle \phantom{\rule{0.167em}{0ex}}}\sigma $ 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*.