Abstract: Field studies were conducted on a sandy soil during spring of 2004 and 2007 in an arid region of southern Tunisia to determine the effect of water quality and nitrogen on yield, yield components and water use efficiency (WUE) of "Spunta", a potato (Solanum tuberosum L.) cultivar. Irrigation water of two qualities viz., canal water (3.25 dS m¹) and saline water (5.2 dS m¹) was used. Nitrogen was applied at the rate of 0, 100, 200 and 300 kg ha^-1. For all treatments, irrigations were scheduled when readily available water in the root zone (35% of the total available water) was depleted. Yield, yield components, water supply and soil salinity were measured. Findings are globally consistent between the two experiments. Results showed that soil salinity values remained lower than those of ECiw and were lowest under emitters and highest midway to the margin of wetted bands. Potato yield significantly decreased under the use of saline water. The reduction in potato yield was mainly attributed to reduction in the number of tubers per m² and tuber weight. WUE decreased significantly with increasing irrigation water salinity. Potato yield, yield components and WUE increased with an increase in nitrogen rates. The N application rate of 300 kg ha^-1 gave good yield and higher WUE of potato in Southern Tunisia.