Land clearing and the intensification of agricultural activities have led to the production of marginal soil, but these changes in land-use management also impact the regional and global carbon (C) cycle.  Rehabilitating degraded pasture with rubber tree (Hevea brasiliensis) plantations, and the effectiveness of these plantations to sequester C, has not been fully evaluated to date.  This study quantified the C sequestered in above- and below-ground tree components in 3.5, 5.5 and 15-year old rubber tree plantations established on former pastureland.  Soil organic C (SOC) stocks were quantified in each rubber tree plantation and compared to a pasture.  The carbon dioxide (CO₂) fluxes during the wet and dry seasons, in the rubber tree plantations and the pasture, were also assessed.  Results showed that  the 15-year old trees sequestered the greatest amount of C in tree biomass followed by the 5.5 and 3.5-year old systems, and showed a significant (p<0.05) linear relationship between diameter at breast height (dbh) and tree C content.  Soil organic C stocks were greater to a 35 cm depth in the 15-year old rubber tree plantation than in the younger plantations and the pasture.  The entire soil profile of the rubber tree plantations and the pasture showed a d¹³C shift to that of C₃ residue, reflecting the greater input of residues from C₃ plants.  CO₂ flux measurements showed that 15-year old rubber tree plantations have a lower rate flux of this greenhouse gas during the daytime in the summer season compared to the pasture.  The results from this study highlight the potential of rubber tree plantations, established on former pastureland, to enhance soil quality and to sequester C for mitigation of atmospheric CO₂ emissions.