Acacia mangium is the major species used in the forest plantation industry due to its fast-growing feature. However, there is still a lack of research on the nutrient concentration, specifically nitrogen (N) and phosphorus (P), as well as carbon content in Malaysia’s forest plantations. Hence, this study aimed to assess the total N and P concentrations in the soil and forest litter. Carbon content in different ages (Year 2, Year 4, and Year 9) of A. mangium plantation (together with a natural forest as a comparison) was also determined. This study was conducted in a Licensed Planted Forest, Bintulu, Sarawak, Malaysia. The natural forest was a control variable in this study. The Kjeldahl method was used to determine the total N. In contrast, dry ashing and double acid (Mehlich-1) methods were used to determine the total P in forest litter and available P in forest soil. The allometric biomass equations were used to estimate the carbon content. Total N in forest litter and forest soil was similar in all treatments. Total P in the Year 4 stand was significantly higher than in the Year 2 stand, yet, no differences were observed when compared with the control. Whereas soil available P showed no significant difference among all treatments. Acacia mangium stands recorded significantly lower total carbon content compared to the control. Old plantation stands contained much more total carbon stock than the younger stands. Also, deadwood is important in determining total carbon stock when it can account for almost 59% of above-ground biomass (AGB) carbon stock. This study revealed that forest plantations could function well in providing an adequate supply of available nutrients as well as have a potential role in carbon sink.