The services would from now on be free for children up to 15 years old and to pregnant women, said Health Minister Emilienne Raoul at the Brazzaville children's hospital at the launch of new campaign.
But she warned: "The medicines are for the sick and must not end up on the streets and in neighboring countries."
The theft and resale of medicines on the black market by hospital staff is a major problem in Congo.
Treatment for tuberculosis, one of the infections linked to HIV, is already free of charge here. TB, malaria and HIV/AIDS are the three top killers in Congo.
Malaria alone kills 21,000 children under five every year, according to the United Nations Children's Fund (UNICEF).