Within the scope of the NUMEX experiment in tropical montane forests of South Ecuador, we assessed phosphomonoesterase and phosphpdiesterase activity. We tested whether phosphatase activity was affected by moderate P and N fertilization along an altitudinal gradient (1000, 2000, and 3000m a.s.l.). Therefore, we sampled the organic layer and mineral soil of fertilization (N, P, N+P) and control plots.