The area of Niari-Nyanga, divided between Congo-Brazzaville and Gabon, corresponds to a Neoproterozoic synclinal whose schisto-limestones and dolomitic layers shelter many caves as well as vast underground karst systems that are hardly known. In a sub-equatorial climate characterized by sparse rainfall with very variable intensity, a dry season of five months and a savanna environment, the endokarst presents a vast array of forms with sometimes large, sometimes small dimensions. The caves are mostly horizontal and oriented along tectonic lines. Old fossil perched caves contrast with epiphreatic caves and drowned inaccessible systems. In current bioclimatic conditions, corrosion seems not very effective and not in equilibrium with some vast morphologies. The stacked levels, the presence of fossil speleothems and detritic material suggest a polyphase genesis in link with important paleoclimatic changes, where humid and dry periods alternate. Recent age dating with 14C on stalagmites show that the speleothemes are holocene and grew during the important rainfalls of this time, before drying up at the general chlimate change 3000 years before present. Thus, the endokarst of Niari-Nyanga as well as its neighbours is an archive of large importance.