To study the influence of nitrogen sources and potassium levels on growth, yield and chemical constituents of lettuce plants, cv. Balady, two experiments were conducted at Experimental Farm of Barramoon, Dakahlia Governorate during the winter  seasons of 1999/2000 and 2000/2001. twelve treatments representing all possible combinations of three N sources (Urea, ammonium nitrate and ammonium sulphate) and four K doses (0, 20, 40 and 60 kg K₂O  / fed.) were used in split plots design with four replicates. The obtained results can be summarized as follows:-   Vegetative growth and yield: 1. Effect of N-sources: Urea followed by ammonium nitrate were significantly increased growth and yield parameters (plant height, No. of outer and inner leaves, fresh and dry weight of outer and inner leaves, fresh weight / plant and total yield, ton/fed.) with no considerable differences among them in most cases. Ammonium sulphate was of the significant least effect.   2. Effect of K levels: Increasing K-levels from 0 up to 60 kg K₂O/fed. considerably increased all the studied growth and yield parameters, 60 kg K₂O level was the most superior one.   3. Effect of interaction: Interaction significantly affected growth and yield of lettuce plant, NH₄NO₃  x 60 kg K₂O/fed followed by urea x 60 kg K₂O/fed were the most superior treatments in their effect with no significant differences among them in most cases. K level (0 K₂O/fed) x all N-sources used were the treatments of the significant least effect.   Chemical constituents 1. Effect of N-sources: Both urea and ammonium nitrate were significantly improved N, P and K content of lettuce plant relative to ammonium sulphate with no considerable differences among them in most cases in the two seasons of study. On the other hand, urea was of the least NO₃ content in their plant leaves. Ammonium nitrate was of the significant highest NO₃ content in both seasons.   2. Effect of K-levels: N, P and K content considerably increased along with increasing the supplied K from 0 up to 60 Kg K₂O/fed. NO₃ accumulation was increased with increasing K from 0 to 40 kg K₂O/fed, then decreased at 60 kg level.   3. Effect of interaction: K 0 level with all N-sources were the treatments of the lowest N, P, K and NO₃ content relative to other treatments. NO₃NH₄ and urea x 60 kg K₂O/fed were the treatment of the highest N, P and K, meanwhile, urea x 60 Kg K₂O was of low NO₃ content. Finally, it could be concluded that ammonium nitrate and/or urea each with 60 kg K₂O/fed were the best treatments for maximizing the growth and yield of lettuce plant. Urea with 60 kg K₂O/fed was the treatment of best yield and low NO₃ content of leaves. So, it concluded as best treatment on basis of yield and NO₃ safety level  for human nutrition.