The southern African regional bloc which brokered a coalition pact in Zimbabwe on Sunday handed the constitutional referendum a clean bill of health despite isolated incidents of violence ahead of the vote.
Saturday's vote, which is set to endorse the constitution that will pave the way for elections, was "peaceful and credible", said Bernard Membe, Tanzania's foreign minister who headed the Southern African Development Community (SADC) observer mission.
"This is a major step in the implementation" of reforms agreed under a power-sharing government between President Robert Mugabe and his long time rival Morgan Tsvangirai.
SADC, which deployed 120 observers, however raised concerns about incidents of violence and intimidation citing an attack on Tsvangirai's activists on the eve of the vote in Harare's Mbare township.
It urged police to take action and arrest perpetrators.