More than 100 people are missing after the accident on the Oubangui River. A local official said 22 passengers had been saved.
The accident happened on Tuesday night when the boat hit a rock, said Mathieu Bela, an official in North Oubangui.
Overcrowded boats frequently sink on DR Congo's network of rivers and lakes.
"There are no signs or signals, which does nothing to help navigation," said Mr Bela.
The boat reportedly sank near Gbongi, in Bosobolo territory, near the border with the Central African Republic.
UN-sponsored Radio Okapi said the boat had been carrying a total of 182 passengers from both countries.