President Museveni received a rousing welcome from the crowd at the Amahoro Stadium.
African leaders are in the Rwandan capital Kigali to attend the inauguration ceremony of President Paul Kagame.
Mr Kagame won a third seven-year term in a landslide victory on August 4.
Among the heads of State present are East African leaders Yoweri Museveni of Uganda, Kenya's Uhuru Kenyatta and Ethiopia's Prime Minister Hailemariam Desalegn.
Tanzania is represented by former president Benjamin Mkapa.
Others African leaders include Sudan's Omar al-Bashir, Idris Deby of Chad, Macky Sall of Senegal, Ismaïl Omar Guelleh (Djibouti), Ali Bongo (Gabon), and acting Nigerian president Yemi Osinbajo.
President Museveni received a rousing welcome from the crowd at the Amahoro Stadium.
President Kagame garnered 98 per cent of the total votes cast against opposition Democratic Green Party flagbearer Frank Habineza and independent candidate Philippe Mpayimana.
The 59-year-old has ruled Rwanda since 2000.