To estimate the optimum and effective amount of nitrogen fertilizer for quantity and quality improvement of three new durum wheat lines, this research was conducted in Gachsaran Dry-land Agricultural Research Station for a duration of 4 years (2003-2007). The study was performed as a factorial expriment, using a randomized complete block design with 4 replications. Two factors of: 4 nitrogen rates [0 (N0), 25 (N25), 50 (N50) and 75 (N75) kg ha-1] and three durum wheat lines (L1: 43210 Karaj (Capieti), L2: MNA-1/RMF7 and L3: SORA/2 * PLATA-12) were taken into condsideration. Results indicated that nitrogen rates exherted significant effects on plant height, spike length, number of spikes/m2, number of grains/m2, harvest index, grain yield as well as grain protein content. There was a significant difference among these three lines in the above respects. Capieti (L1) bore a higher number of grains per spike (50.52), harvest index (46.15%), higher grain yield (3.491 t. ha-1) and grain protein content (11.63%) followed by line L2. Among these lines, L2 had a higher plant height (86 cm) and with respect to spike length, the two lines of L2 and L3 produced the longer and the shorter spikes respectively. On the other hand, nitrogen rates presented significant differences in all the evaluated traits with the exception of 1000-grain weight and harvest index. Higher grain yield (3.85 t. ha-1) and higher grain protein content (12%) were obtained from the nitrogen treatment of N75. The study on relation of grain yield and harvest index indicated that for each 1% increment of harvest index, grain yield increased approximately 0.076 t ha-1. Finally, to obtain higher grain yield per unit area, higher grain protein content and for prevention of further environmental pollution caused by inappropriate application of nitrogenous fertilizers, a pure nitrogen rate of 75 kg ha-1 with application at planting time is recommended for these new lines at this site as well as for other similar regions.