Ernest Musafiri, a Kabila supporter, said: "This December 6 is a day of joy for us," said
He recalled campaign promises made by the president to unite and reconstruct the country, which is a former Belgian African colony and was in a civil war between 1998 and 2003.
"We have to have confidence in him," he said.
Kabila won the vote largely due to his support in the east, where his fellow Swahili speakers credit him with ushering in the peace plan that brought the war to an end.
The 35-year-old has been acting president since 2001 when he took over after his father was assassinated.
Reflecting on the poll, supporters of Jean-Pierre Bemba, who lost in the presidential election against Kabila, said they felt Kabila had been fraudulently elected.
"So be it. We bow down, but we'll be watching to see what he achieves. In five years' time, we'll give our verdict," said Norbert Kabuya.
DR Congo's first free elections in more than 40 years cost the international community about half a million dollars. They were protected by the world's biggest UN peacekeeping force.
The ceremony was held outside a courthouse which was set on fire two weeks ago when fighting broke out among Bemba supporters who had gathered to back their candidate's unsuccessful legal challenge of the election results.
Kabila has pledged to be the leader "of all the people, without distinction", but controlling the various armed groups in the east could be his most significant challenge.
Clashes in the east
Tabaro Kiconco, the army spokesman for western Uganda, told Reuters news agency on Wednesday: "Yesterday, after that fighting started, over 12,000 refugees fled to the Ugandan side and are currently camped in two places."
He said refugees would have to register with the local authorities to be allowed to stay.
"The refugees must identify themselves so we know they are not a security threat."
At least 12,000 people have fled across the border into southwest Uganda to escape clashes between government forces and rebel soldiers, a Ugandan army spokesman said.
The fighting broke out last month when forces led by General Laurent Nkunda attacked government soldiers near the town of Sake.
UN peacekeepers became involved and more than 150 rebels were killed as they used helicopter gunships, heavy weapons and armoured vehicles to fight back the offensive.
|UN peacekeepers have clashed with rebel |
soldiers led by General Laurent Nkunda
Colonel Delphin Kahimbi, deputy head of the Congolese army in North Kivu province, told Reuters on Tuesday: "We are still finding bodies, but so far we have found more than 150.
"They [the rebels] were hit hard by the UN's helicopters and tanks."
Indian UN soldiers were forced to fight after poorly equipped and disorganised government troops withdrew during attacks by the rebels, who were threatening the town of Goma.
Colonel Bernard Byamungu, Nkunda's operations commander, and Dieudonne Kabika, the secretary-general of his political movement, surrendered along with nine other fighters to the UN.
A senior UN officer described Byamungu's surrender as "a huge catch" and he was handed over to government forces.