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The mangrove ecosystem in Kutai National Park (KNP) has an important and strategic role. Maintaining the integrity of mangroves as a conservation area needs to be improved, one of which is by recognizing floristic potential. The study was carried out on TNK mangrove forests in the East Kutai Regency, to find out the composition, importance value and diversity index. Measurements were made on trees with a diameter of ? 10 cm and a plot size of 10 x 10 m as many as 168 plots. KNP mangroves have high species richness, founded total 17 species and each in Lombok Bay 12 species, in Kaba Bay 13 species, and in Pandan Bay Estuary 10 species. The species comes from 6 families with a density 122-202 trees ha^-1, and the highest density was found in Pandan Bay Estuary. Species dominanted, i.e. Bruguiera gymnorrhysa, B sexangular, Ceriops tagal, Rhizophora apiculata, R mucronata, Sonneratia alba, and S caseolaris. The highest Important Values Index ??(IVI), i.e. B sexangular, B. gymnorrhysa, R mucronata, and R apiculata,. Then the highest mangrove diversity index was found in Lombok Bay with value above 0.9, while the other two locations below 0.9. Furthermore, there are also species with density and NPJ is low, i.e. Xylocarpus granatum, Rhyzophora stylosa, Avicennia marina, A alba, and Ceriops decandera.