Selective oxidative decomposition of NH3 (1000 ppm) in water to N-2(wet oxidation) was achieved with precious metal-supported catalysts at 433 K under 8 arm of O-2 without alkalization of the solution. As a support for Pt, an anatase TiO2 (P-25) was superior in activity, while NO2- and NO3- were formed at concentrations of about 3 and 4 ppm, respectively, at 6 h. The activity fur N-2 formation was in the order of Pt > Ru > Pd > Ph >> Cu, Co, and Ni, when the TiO2 (P-25) was used as the support. It,was further found that Pd/TiO2 (P-25) gave 100% selectivity to N-2; no undesirable NO2- and NO3- were detected in the solution nor any N2O in the gas phase. Increase in the loading amount of Pd from 0.25 to 1.0 wt% on TiO2 (P-25) effectively enhanced catalytic activity, while retaining high selectivity.