Tropical forest has a constant renewal of tree mass, becoming irregular sites of great complexity and dynamism. The structural features of these are very important aspect in defining its composition and organization. To characterize the structure of a lowland forest bordering the river Irmalí, Madungandi Region, established a rectangular plot of 1 hectare, divided into 10 subplot of 0.1 ha., recording all trees with DBH ? 10 cm.  The species of most valuable importance in this forest were Tetragastris panamensis, Peltogyne purpurea, Copaifera aromatica, Eugenia sp., Brosimun alicastrum and Astronium graveolens. Tetragastris panamensis is the most important with 11% of the total IVI. There were three tree strata: emerging, composed of trees over 20 m in height, this one recorded 20 individuals, highlighting Copaifera aromatica and Dipteryx oleifera, both with 27 m. in height; canopy or dominant, between 13-19 m, in which 149 individuals were recorded, and the dominant, bellow 13 m. in height, being the layer with higher species richness and abundance of individuals.