We present two models of log-linear equations for biomass estimation in planted stands of 3- to 10-year-old Acacia mangium Willd. trees, using destructive sampling data of 59 trees in West Java, Indonesia. The log-linear equations include parameters for individual leaf, branch, stem, aboveground, belowground (root), and total biomass. Average annual increments of stand-level biomass were estimated at 7.77 to 10.09t ha^<-1> y^<-1> (model A) and at 7.91 to 10.27t ha^<-1> y^<-1> (model B), with the largest values in the 5-year-old stand. Following the methodology presented by IPCC National Greenhouse Gas Inventories Programme, we calculated basic wood density (D), biomass expansion factors (BEF), and root-to-shoot ratios (R) of the study stands. The value of D increased significantly as stand age increased from 3 to 8 years, but did not significantly differ between 8- and 10-year-old stands. The value of BEF did not differ among the 3- to 8-year-old stands (average 1.332) and decreased to 1.180 in the 10-year-old stand. The values of R increased significantly with stand age, from 0.157 to 0.190. The BEF values of A. mangium in this study were smaller than the default values for the tropical broad-leaf forest type (dbh>10cm) given by IPCC (mean, 3.4; range, 2.0-9.0). Because many factors may affect the parameter values of log-linear equations and D, BEF, and R for biomass estimation, the equations and values provided in this study are only applicable to A. mangium forests growing under comparable climatic, stand age, forest management conditions.