The Kayongozi River (French: Rivière Kayongozi) is a river in Burundi, a right tributary of the Rurubu River.

The Kayongozi River forms near the border with Tanzania in the north of Cankuzo Province, then flows southwest into Ruyigi Province. It continues southwest, then turns to flow northwest to it mouth on the Ruvubu River. Tributaries include the Nyamashishi and the Rugasari.

The surroundings of the Kayongozi River are mainly covered in savanna forest. The area is quite densely populated, with 111 inhabitants per square kilometer as of 2016. The average annual temperature in the area is 19 °C (66 °F). The warmest month is September, when the average temperature is 22 °C (72 °F), and the coldest is April, with 18 °C (64 °F). Average annual rainfall is 1,321 millimetres (52.0 in). The rainiest month is December, with an average of 215 millimetres (8.5 in) of precipitation, and the driest is July, with 1 millimetre (0.039 in) of precipitation.

The Kayongozi basin contains 3,410 hectares (8,400 acres) of marshland, of which 1,979 hectares (4,890 acres), or 58%, had been developed as of 1998.

The Kayongozi Small Hydropower Plant in Ruyigi with 500kW was initiated in 2013, to be operated by the Rural Electrification Agency (ABER). The Kayongozi micro-hydroelectric power plant in Ruyigi was inaugurated on 18 December 2014. A 2012 report listed three other potential hydroelectric sites on the river: KAYO 028, with 2.5MW, KAYO 027 with 2.5MW and KAYO 002 with 1.8MW.

In July 2024 the log bridge over the Kayongozi River which links the Kavumu and Murehe collines of the Commune of Cankuzo, Cankuzo Province, was almost unusable. Commerce was disrupted and children had dropped out of school. The provincial governor was aware of the problem, but did not have the budget for a modern bridge. In the meantime he recommended that the residents do what they could to repair the bridge using wood.

• List of rivers of Burundi