Current knowledge, although significant, does not yet provide a full understanding of the functioning of swamp forests in Central Africa. The aim of this study was to estimate the species importance value index (IVI) and characterise the stand structure of three forest types in the Likouala swamp forest in the north of the Republic of Congo. The forest inventory was carried out in flooded forest (FF), periodically flooded forest (PFF) and terra firme forest (TFF), focusing only on trees with a diameter of 10 cm or more. In each forest type, species of very high ecological importance value made up more than 56% of the species recorded, and their numbers increased as we moved from TFF to FF, with a marked predominance of sciaphyte species. This dominance was corroborated by the inverted J-shaped distribution curves observed in the three types of forest, indicating good natural regeneration. Furthermore, the mean values for stem density per hectare decrease from FF (445±8 stems/ha) to TFF (351±13 stems/ha), while those for basal area and height tend to increase in the same order, from 30.00±2.1 m2/ha to 35.46±3.2 m2/ha and from 20.26±4.20 m to 26.10±5.82 m respectively. In short, the low representation of pioneer species suggests a gradual evolution of each type of Likouala swamp forest towards a mature stage, characterised by a physiognomy dominated by sciaphyte species.