The objective of this study was to investigate the effect of three plant densities (33, 44 and 55 plants /m2) and three phosphorus levels (15.5, 31 and 46.5 kg P2O5 /feddan) (feddan = 0.420 hectares = 1.037 acres) on yield, components and seed protein percentage of lupin cv. Giza-2. Two field trials were carried out at the Agricultural Experimental Farm of Al-Azhar University, Assiut governorate, Egypt, during two successive seasons of 2018/2019 and 2019/2020. Split plot design was used with three replicates; where plant density treatments were assigned to the main plot, while phosphorus levels were distributed randomly in the sub plot. The main effects could be summarized as follows: The results indicated that increasing plant population densities from 33 to 55 plant /m2 measurably tended to increase plant height and protein percentage, whereas reduced number of branches /plant, number of pods /plant, number of seeds /plant, 100- seed weight, seed yield /plant and seed yield /feddan. Seed yield per feddan reached its maximum with sowing 33 plant /m2 (20 cm between hills) in both seasons. Increasing phosphorus fertilizer levels from 15.5 to 46.5 kg P2O5 /feddan increasing all studied traits in both seasons, where the highest values were obtained from the application of 46.5 kg P2O5 /feddan in the two experimental seasons. The interaction effect between plant density and phosphorus fertilizer levels had significant effect on seed yield per feddan and seeds protein content in both seasons and plant height and number of pods per plant in the first and second seasons, respectively. Therefore, the study recommends population density 33 plant /m2 and phosphorus fertilization at the level of 46.5 kg P2O5 /feddan, in order to improve the production of lupin under the conditions of Assiut governorate, Egypt.