The study estimated the carbon stock contents of a lowland rainforest in Nigeria, Okomu National Park. Four major Carbon pools were estimated, they were: above-ground biomass; below-ground biomass: dead wood; and litter. Nested plot design was used for sample plot demarcation. All trees (living and dead) with Dbh ≥ 10cm were enumerated within the 50 m X 50 m and 20 m X 20 m plots, while the 1 m X 1 m quadrant was for litter samples collection. Core samples and sub-samples were collected from live tree and dead wood respectively. The total carbon stock estimated for the study area was 177.58 tons/ha, of which above-ground biomass accounted for 134.01 tons/ha and below-ground biomass was 33.50 tons/ha. Dead wood was 6.05 tons/ha while litter was 4.02 tons/ha. The Carbondioxide equivalent was estimated to be 651.14 tons/ha. The monetary value for the carbon stock estimated at 4/tCO2was 52,674,679. Thus, carbon sequestration is one of the significant ecosystem services provided by mature rainforests. Keywords: Carbon pool, Rainforest, Ecosystem Service, Climate Change, Forest Management DOI: 10.7176/JRDM/63-06 Publication date:March 31st 202