Well, i know about 8 differences:
1. Athenians were divided into 10 tribes, however Americans are
divided into 50 states
2. Athenians elected 50 men from each tribe, however Americans
elect by population
3. Athenians had a direct democracy (participated directly),
however Americans have a representative democracy (elect
4. Athenians had the Council of Five Hundred, however Americans
have the Government
5. Athenians limited electing and voting rights to just men,
however Americans have electing and voting rights to men and
6. Athenians had slaves, however Americans don't have slaves
(well, they used to until 1863 when all of the slaves were freed by
7. In Athens, women stayed at home and work, however in America,
women participate in all kinds of daily activities, even in the
8. In Athens, slaves were just captured war prisoners, however
in America, slaves were Africans who were treated as property due
to their dark skin.
Athenian democracy was not the Rule of the People, but the Rule
of the Demos, hence the name. Many people living in ancient Greece
were not part of the demos, most prominently of course, slaves.
Also, just about everything else.
There are two key differences between the type of democracy
practices in ancient Athens, and modern American democracy.
Firstly (and, the largest difference), the Athenians practiced
direct democracy - citizens were expected to vote themselves
on topics facing the government (and courts). The United States is
a representative democracy - citizens elect one citizen to
act as their proxy (representative) in the larger government.
Secondly, citizenship in ancient Athens was significantly more
restrictive, and far less than the majority of residents of Athens
held citizenship. Athenian citizenship was based on age, gender,
and to a certain extent tribal membership and wealth, with the
right to vote being even further restricted; in addition, Athens
practiced slavery. American democracy is a form of universal
suffrage, meaning that everyone is a citizen, and that the only
real restriction on voting is a minimum age (though voting is
restricted for certain peoples, mainly felons and the mentally
As to the actual implementation of the governments, Athenian and
American government are radically different. See the links below
for a better description of both forms of government, as the
structural differences are too extensive to summarize here.
Original Greek "democracy" and current American "democracy" have
few differences. In the Greek form only the elite could participate
in the process of important decisions. In the US form only tiny
group of elitists may make important decisions. Neither of them are
actually democracies. Democracy's original meaning was "the people"
"to rule." It meant that the will of the majority of the governed
would become the supreme law of the land. That condition has never
existed within any country on Earth simply because humanity has
never before had the technology to define the true will of a
population regarding all the issues that may affect them.