Wet air oxidation (WAO) was applied to treat the desizing wastewater from natural and manmade fiber processing in a 2-L autoclave reactor. The range of operating temperatures examined was between 150 and 290 degrees C. The partial pressure of oxygen ranged from 0.375 to 2.25 MPa at a reference temperature of 25 degrees C. Variations in chemical oxygen demand (COD) and total organic carbon were monitored during each experiment and used to evaluate the performance of the reaction process. Experimental results showed that WAO is an efficient method for the treatment of desizing wastewater. A higher COD removal was achieved under gentler reaction conditions with the aid of a catalyst. A two-parameter mathematical model involving a fast reaction and a slow reaction was used to describe the WAO reaction kinetics and to calculate the reaction activation energies.