Small groups scattered across the capital, some of them holding Bibles and rosaries, held a minute of silence for the victims of the civil unrest in the Kivu region before breaking into song and prayer.
“No to the balkanisation of the DRC,” read one placard.
Former rebels who had been integrated into the regular army and defected again earlier this year have been battling government troops since May in the eastern DR Congo.
The fighting has displaced more than 200,000 people and sparked fears of a fresh regional escalation, amid allegations the mutineers are supported by neighbouring Rwanda.
The Catholic church wields tremendous influence in the vast resource-rich and conflict-prone central African country.