Digestibility and feeding trials were conducted to investigate the effect of ground date seeds (GDS) as a partial replacer for ground maize (GM) on nutritive values, nitrogen metabolism, and lambs performance.  Four mature Ossimi rams of 40 ± 1.45 kg live body weight (LBW) were used in digestibility trials and sixteen Ossimi growing male lambs with an average LBW of 19.88 ± 0.86 kg were used in group feeding experiment for 120 days.  The diets used in both experiments were concentrate feed mixture (CFM) + wheat straw (WS) that represent 1% of LBW as a control diet ( D1 ), while 15, 30 and 45% of ground maize (GM) in (CFM) were substituted by ground date seeds (GDS) for diet 2 (D2), diet 3 (D3) and diet 4 (D4), respectively.  The results of the digestibility trials revealed that replacing the GM with 15, 30 or 45% GDS was associated with a significant increase in CP, EE, CF and NFE digestibilities.  The corresponding nutritive value expressed as total digestible nutrients (TDN), starch value (SV) and digestible crude protein (DCP) % were increased significantly (P ≤ 0.05) with GDS inclusion the diet.                 There was significant (P ≤ 0.05) increase in nitrogen balance (NB) with GDS  treatments compared to the control group.  Also nitrogen absorption (NA) was increased significantly (P  ≤ 0.05) in the diets containing GDS, the values were 11.90, 12.13, 12.14 and 12.23 g / day for D1, D2, D3 and D4, respectively. Significant increase (P  ≤ 0.01) were recorded in total gain and daily gain for lambs fed containing GDS diets.  Total dry matter consumed along the whole feeding period was significantly differed (P ≤ 0.01) among groups, being 129.84, 135.91, 139.39 and 143.51 kg for D1, D2, D3 and D4, respectively.  Feed conversion ratio expressed as kg feed / kg gain was in favor of lambs fed D3 (6.49) than those fed D2 (6.71) compared with 6.83 for D1 and 7.18 for D4.  The economical view was improved (P ≤ 0.01) due to GDS inclusion in the diets.  Results indicated that ground date seeds could be used up to 30 % of the ground maize in the feed mixture of sheep without any adverse effects.