PhOH was oxidized in aq. soln. with air O-2 at 393-433 K and 1.85 MPa on activated C in a trickle-bed reactor at flow intensity of liq. and gaseous phases 0.17-1.77 and 0.2-0.62 kg/m(2)s, resp., to det. the catalytic activity of the bed as well as the proces yield and selectivity. A math. model of the process was formulated and verified by using authors' own exptl. data base. A possibility of improving the efficiency of the process by periodically changing feeding of the bed with liq. using on-off method was checked. Neither any significant increase in the PhOH conversion nor any change in the process selectvity were achieved.