The freshwater swamp forest in Bonny Rivers State, Nigeria was investigated to determine the forest structure and phytodiversity. Four 250x40 m transects containing five (10x10 m) randomly laid quadrats were used in 1 hectare plot to increase the chances of encountering and inventorizing all species. Phytosociological data were collected and used to determine diversity of the forest. Ninety four plant species belonging to 40 families (14 shrubs, 26 trees and 54 herbs) were encountered which represents 14.89% shrubs, 27.66% trees and 57.45% herbs in the forest. The four most diverse families in descending order were Euphorbiaceae (10 species), Poaceae (8 species), Araceae (7 species) and Papilionoiaceae (4 species). 19 families were represented by only one species. Species density ranged from 30 species ha-1 in Icacinaceae to 3010 species ha-1 in Euphorbiaceae. Smilaceae and Icacinaceae with relative frequency value of 0.498 were the least frequent families while Dioscoreaceae Family Importance Value (FIV) of 0.016 was the least in the survey. Secondary forest tree species (Anthocliesta vogelii, Elaeis guineensis, Harungana madagascariensis and Musanga cecropioides) and fruit trees (Musa sp, Psidium guajava, Mangifera indica and Cocos nucifera) were identified which confirmed anthropogenic incursions at different times into the pristine forest. The need for conservation therefore cannot be overemphasized.