Two field experiments were carried out at the Agric. Exp. and  Res. Stat., Fac. Agric., Cairo Univ., during 2004/2005 and 2005/2006 seasons to study the effect of three plant densities (33 , 44 and 55 plants/m²), three phosphorus levels (15.5 , 31 and 46.5 kg P₂O₅/fed) and three nitrogen levels (25 , 40 and 55 kg N/fed) on yield and its components of lupin (Giza 1). The main effects could be summarized as follows: The results revealed that the lowest density i.e. 33 plants/m² gave significantly the highest number of branches and pods/plant, seed yield/plant and seed index , but the shortest plants with the fewest number of seeds/ pods and the lowest averages of seed yield/fed and seed protein content. Increasing phosphorus from level 15.5 to 46.5 kg P₂ O₅/fed increased yield and its components. The seed yield/fed was increased as applied P₂O₅ level was increased up to the highest level i.e. 46.5 kg P₂ O₅/fed. Adding phosphorus at a level of 46.5 kg P₂O₅/fed increased seed yield/fed over the plants fertilized by 15.5 or 31 kg P₂O₅/fed levels by 20.23 and 3.89 %, respectively as average of the two seasons. Increasing nitrogen from 25 to 55 kg N/fed increased all studied components. Application of 40 kg N/fed increased seed yield/fed., over the 25 kg N/fed level by 39.72 % where the further increase of N level caused insignificant increase in seed yield/fed. The interaction between the three studied factors had significant effects on seed yield/plant and per feddan in both seasons. The highest significant seed yield/fed was recorded from sowing at plant density of 55 plants/m² and fertilization with 31.0 kg P₂O₅/fed and 40 kg N/fed.