This investigation was carried out at Gemmeiza Agriculture Research Station Farm, Gharbeia Governorate during 2006/2007 and 2007/2008 onion growth seasons. The objectives of this study was aimed to study the effect of four irrigation regimes (one, two, three and four irrigations) and six onion cultivars selected by Onion Research Section (Composite 9, Giza white, Behairy no pink, 1866 Globe, Giza Red and Giza 20) on internal bulb quality. A separate experiment for each irrigation treatment was used Randomize Complete Blocks Design in four replications. The main obtained results from this investigation cane be summarized as follows: 1-   Average weight of bulbs, average number of growing points and average number of complete rings increased with every increase of irrigations up to 3 irrigations. Whereas, total soluble solids and average percentage of dry matter decreased with  every increase of irrigations. Shape index and stem plate diameter were not affected by irrigation regimes. 2-   Giza 20 and Comp. 9 cultivars have the heaviest bulb weight followed by Giza Red. Whereas, Giza White have the lowest bulb weight. Behairy no Pink and 1866 Globe cultivars were nearly globe. Shape index and the another tested cultivars seemed to be thick flat and highly thick flat shape index. Giza White and Giza 20 cultivars have the widest stem plate diameter, whereas, 1866 Globe and Behairy no Pink cultivars have the lowest stem plate diameter. Giza Red and Giza 20 cultivars have the highest number of growing points/bulb. 1866 Globe cultivar have the highest average number of complete rings/bulb. Whereas, Giza 20 cultivar have the lowest average number of complete rings/bulb. Giza White cultivar  have the highest values of total soluble solids. Whereas, Comp. 9 cultivar have the lowest values of total soluble solids. Giza White cultivar  have the highest values of dry matter content followed by Giza 20 and Giza Red. Whereas, Comp. 9 cultivar  have the lowest values of dry matter content in bulbs.      3-   The interaction between irrigation regimes and cultivars showed significant effects on average stem plate diameter/bulb in the second season of study. Giza White have the widest stem plate diameter when gave three irrigations.