According to the Electoral Commission, President Museveni won 59 per cent of the vote, well ahead of his main rival Kizza Besigye on 327 per cent.
Mr Besigye claims the results were marred by massive fraud and has refused to accept them.
Opposition supporters gathered outside Mr Besigye's Forum for Democratic Change headquarters in Kampala.
Police fired tear gas in an attempt to disperse the demonstration.
The election was Uganda's first multi-party poll in 25 years and was seen as a test of its democratic credentials.