Two experiments were conducted to determine the effects of graded levels of rubber seed meal (RBSM) and rubber seed oil (RBSO) on energy, dry matter and nitrogen (N) digestibility, and N retention of growing rats. In the first experiment, RBSM replaced 25, 50, 75 and 100;RBSM substitution was either unsupplemented or supplemented with amounts of DL-methionine and L-lysine calculated to make up their concentrations to the minimum recommended National Research Council levels. In the second experiment, maize oil (MO) and RBSO replaced maize starch at 3, 6 and 9;in a 2 X 3 factorial arrangement treatments. The diets in both experiments were iso-nitrogenous, containing 17;(Experiment 1) and 15;(Experiment 2) crude protein on a fresh weight basis. In Experiment 1, significant reductions were obtained in dry matter, energy and N digestibility, in absolute N retention and in the percentage of digested N retained (P<0.01) as the level of RBSM increased. Supplementation of the 100;RBSM protein diet with methionine and lysine did not reduce the depressions in the digestibility of energy, dry matter and N, but it significantly improved N retention. In Experiment 2, the inclusion of RBSO at the three levels did not affect the digestibility of dry matter, N or energy, or N retention.