The swearing in of Joseph Kabila as president of the Democratic Republic Congo was broadcast on state television and afterwards Mr Kabila addressed the nation.
The crowd at the event was in high spirits, with Mr Kabila promising respect for human rights and a new era for the war-ravaged nation.
President Kabila married Olive just before the election campaign. The couple have a daughter born in 2001.
There was much fanfare with the country's Supreme Court judges attending in uniform.
Jean-Pierre Bemba who lost the run-off election refused to attend, but a presidential loser in the first round, Azarias Ruberwa, was amongst the guests.
Diplomats offered their congratulations after the event.
Nine African heads of states were also there, including Omar Bongo of Gabon - Africa's longest-serving leader.
Thousands of guests sheltered from the hot sun in the gardens of State House, just next to the huge and powerful Congo river, under umbrellas.