Abstract: This study was done as factorial based on Randomized complete block design with three replications in 2006 in research field of Mohaghegh Ardabili University, Ardabil, Iran. First factor was nitrogen level (0, 80, 160 and 200 kg ha-1 net nitrogen) and second was tuber size (<40, 40-80 and >80 g). Results showed that tuber size increase and nitrogen usage reduced Agronomical Nitrogen Use Efficiency (ANUE) and increased Physiological Efficiency (PE), Apparent Recovery Efficiency (ARE) and Nitrogen Use Efficiency (NUE). The most tuber yield, total plant dry matter, number of tuber per plant, mean tuber weight and tuber dry weight were achieved in medium tuber size. Also, the most tuber yield, mean tuber weight and tuber dry weight were gained at 160 kg ha-1 net nitrogen. Utmost nitrogen uptake by plant and total plant dry matter was observed at 160 kg ha-1 nitrogen. So, utilization of 160 kg ha-1 nitrogen with medium tuber size in order to achieving most yields, planting and eating usages is recommended.