Resumo. The objective was to estimate the biomass and organic carbon in Araucaria angustifolia stands with different ages. The Araucaria angustifolia stands studied were not pruning but were thinning in difference ages. In stands of 32 and 31 years-old, were three thinnings. In stands of 30, 29, 25, 24 and 23 years-old, were two thinnings. Biomass avaliation was conducted according to the destructive method, using the sampling of seven trees were randomly distributed in each stand. The plants were harvested, after were obtained the dendrometric variables: DBH, total height and commercial height (minimum diameter of 8 cm). Stand with 23 years had the highest volume of stem wood (613.02 m3 ha-1), followed by 30, 31 and 32 years-old stands (418.41, 520.21 and 518.48 m³ ha-1), respectively. However, in terms of stem biomass the results were similar, 23 years-old stand had 138.02 Mg ha-1 and 30, 31 to 32 years-old totaled 118.77, 128.97 and 155.01 Mg ha-1, respectively. In Araucaria angustifolia stands the total stock biomass and organic carbon in different ages ranged from 60.72 to 289.84 Mg ha-1 and 21.73 to 123.86 Mg ha-1, respectively. Plant densitie and thinning intensity were directly influenced the biomass and carbon stored.