Two field experiments were carried out in Tag AL-Ezz, Agricultural Research Station, Dakahlia Governorate, Agricultural Research Center, Egypt, during 2007/2008 and 2008/2009 seasons to determine the effect of two storage methods (normal and cold), three mother bulb sizes (large, medium and small) and three harvesting times of seeds (early, intermediate and late) on onion growth, seed yield and its components as well as seed quality. The main results of this investigation could be summarized as follows: o Storage onion bulbs at 5 °C for 2 months produced the highest values of growth, seed yield and its components and also high seed quality in both seasons. o Planting large size of mother bulb resulted in the highest values of growth, seed yield and its components and also high seed quality. However, medium size of bulb might be recommended due to economic consideration. o Harvesting time had a significant effect on number of leaves/plant and root length (in the first season), number of scapes/plant, seed head weight, number of flowers/seed head, number of seeds/seed head, weight of seeds/seed head, seed yield/plant and seed yield/fed in both seasons. Harvesting onion seeds after 157 days from sowing (medium harvesting time) recorded the highest seed yield and also most its components. o The results recommended storage medium size of mother bulbs at 5 °C for 2 months before sowing and harvesting after 157 days from sowing to raise onion seed productivity and its quality.