This investigation was carried out at the experimental farm of Assiut University in 2004/2005 and 2005/2006 seasons to study the effect of irrigation regime and stage of maturity on onion  Giza 6 cv. storage ability .The quantity of applied water ranged between 350 to 7350 m²/fed..Irrigation interval was 15 or 30 days .Cured bulbs stored at room temperature for180 days.The lowest percent of damage after 90 days was recorded in regime1early harvesting. The highest water quantity resulted in the highest weight loss percent after both  90 and 180 days of storage The lowest percent of total loss after 90 days was recorded in early harvested bulbs under regime 1 which received the lowest water quantity .The height marketable bulbs (%) was obtained after 90 days storage in regimes which received the lowest water supply. Early harvesting resulted in lower total loss and higher marketable percent after both 90 and 180 days of storage .