The effect of packing roughness on the thermal and hydraulic performance of a packed bed wet cooling tower were investigated experimentally. Tower enhancement ratio and air-side pressure drop ratio were determined as functions of packing relative roughness at different values of water inlet temperature, and water-to-air mass flux ratio. The packing used was glass Raschig rings 10 mm thick and 10 mm in diameter. The surface roughness was changed by adhering sand papers of different roughness to the outside surface of the packing. The experimental data showed that an increase in the surface relative roughness from 1 to 5.62 can increase both the tower enhancement ratio and the air side pressure drop ratio up to 146% and 142%, respectively. The effect of the surface relative roughness is more pronounced at lower values of water-to-air mass flux ratio and at higher values of hot water inlet temperature. Also, a new analytical expression was developed to calculate the cooling tower characteristics.