The political opposition has denounced the 27 November vote as rigged and called on opposition supporters to protest.
Electoral authorities today said results from 99 percent of polling stations showed the constitutional reform passing by more than 93 percent.
Official voter turnout in the referendum was reported at some 64 percent, well above the one-third required to make the voting valid.
The proposed constitutional changes have been welcomed by the European Union and the United States.
But the Armenian opposition, which had urged a boycott of the referendum, has alleged that the results are being invented by authorities and has called on supporters to demonstrate at a protest rally today in Yerevan's Freedom Square.
The constitutional changes would include reform of the judicial system and seek to clarify the division of powers between the president, government, and parliament. The changes would also allow members of the Armenian diaspora around the world to apply for Armenian citizenship.
RFE/RL Caucasus Report
SUBSCRIBE For weekly news and in-depth analysis on Armenia, Azerbaijan, Georgia, and Russia's North Caucasus by e-mail, subscribe to "RFE/RL Caucasus Report."