The study was conducted at the three Municipalities of Cotabato province Southern Philippines between January to May 2011. The study aimed at determining the Carbon budget of the different age rubber plantation through field sampling and modeling. Actual field measurement of dbh, were done for the estimation of above-below ground biomass. The major carbon pools, such as above-ground biomass, below-ground biomass, litter and understory vegetation were added and multiplied with 45% default value by IPCC to obtained the carbon density in Mt/ha. The total estimated biomass of the rubber plantation in Antipas were 103.91Mt/ha (10 years) and 573.21Mt/ha (20 years) with carbon density of 46.79Mt/ha and 257.95mt/ha respectively. For the Arakan plantation, the following were revealed in the estimation: (a). the 40 year plantation has total biomass of 1041.54Mt/ha biomass (468.69Mt/ha C), (b). the 11 year plantation has 158.79Mt/ha biomass (71.46Mt/ha C), (c). the 35 year plantation has total biomass of 246.23Mt/ha (110.8Mt/ha Carbon density), and (d). the 12 year plantation has 355.60Mt/ha biomass (160.02Mt/ha C). In Matalam Cotabato, the two different age rubber plantations has an estimated biomass density of 149.47Mt/ha in 8 years with 67.26 Mt/ha C and 70.82Mt/ha biomass density for the 6 year old plantation with 31.87 Mt/ha C.The soil organic carbons found in each plantation were: Antipas; 100.25t/ha (10 years) and 203.54t/ha (20 years), Arakan; 202.55t/ha (40 years), 142.67t/ha (11 years), 86.1t/ha (35 years) and 129.53t/ha (12 years), Matalam; 53.32t/ha (8 years) and 62.04t/ha in the 6 year plantation. T-test reveals significant differences of the biomass and carbon density of the rubber plantation with respect to age range (6-12 years and 20-40 years). This implies that biomass production and carbon storage potentials of rubber plantation is very much dependent on plantation age. Pearson regressioncorrelation analysis of the carbon density of each plantation with carbon pools found to be highly significant.