This investigation was carried out at Shandweel Agric. Res. Station, Sohag, Egypt, from 1996 to 1998 seasons to study the effect of self- pollination and one cycle of selection on some bulb characters and yield components of   Giza-20 cultivar. .             Percentage of single growing point, single center bulbs and those free from pink flesh, were significantly increased in the S₁ population, while percentage of internal doubling, average bulb weight, external doubling, yield of culls and total yield were decreased.             Predicted gain due to selection was more than realized in all selected populations and for all studied characters, except free from pink flesh in the three selected populations.             The differences between predicted and realized responses were significant in all  characters except external doubling, bolting, marketable and exportable yields in the three selected populations.