The effect of superficial gas and liquid velocities upon ozone mass transfer in a co-current upflow reactor filled with granular silica gel is studied. A concentration of dissolved ozone at steady state is observed depending on technological and operating conditions of the reactor. Increase of gas velocity is found to increase both the overall mass transfer coefficient and the concentration of dissolved ozone at steady state. Increase in liquid velocity at fixed gas velocity decreases the concentration of dissolved ozone at steady state. Ozone decomposition in the presence of silica gel is investigated and shown limited to self decomposition in liquid bulk. Ozone mass transfer is modelled from experiments carried out under different conditions of bed height, gas flow rate and liquid flow rate in order to predict the overall mass transfer coefficient involved in further simulations of ozone concentration profiles along the length of packed bed.