An incubation experiment was conducted to examine the effects of the phosphorus (P) application on nitrous oxide (N2O) and nitric oxide (NO) emissions from soils of an Acacia mangium plantation in Indonesia. The soils were incubated with and without the addition of P (Ca[H2PO4]2; 2 mg P g soil−1) after adjusting the water-filled pore space (WFPS) to 75% or 100%. The P addition increased N2O emissions under both WFPS conditions and NO emissions at 75% WFPS. Some possible mechanisms are considered. First, the P addition stimulated nitrogen (N) cycling, and N used for nitrification and/or denitrification also increased. Second, the P addition could have relieved the P shortage for nitrifying and/or denitrifying bacteria, producing N2O and NO. Our results suggest that the application of P fertilizer has the potential to stimulate N2O and NO emissions from Acacia mangium plantations, at least when soils are under relatively wet conditions.