Two field experiments were conducted during the two successive winter seasons of 2004/2005 and 2005/2006 at Siwa Oasis, Khamisa region, Egypt. The aim of the study was to investigate the effect of organic manures and bio-fertilizers on onion (Allium cepa L.) cv. Giza 20 grown on sandy soil irrigated with saline water (about 7000 ppm). Three sources of organic manure (farmyard, sheep and poultry manure) were added to the soil before transplanting at rate of 30, 20 and 10 m3 /fed. respectively. Bio-fertilizers (Nitrobeine, Phosphorene and Nitrobeine + Phosphorene) were used at rate of 3 kg/fed. for each one by dipping onion seedlings in bacterial suspension before transplanting. Growth characters, yield and its components as well as chemical content of onion bulb were recorded. As for the effect of organic manures on vegetative growth of onion plant expressed as plant height, number of leaves per plant and fresh and dry weight per plant, results showed that the best values were obtained with application of poultry manure when compared with other organic manure applications. Moreover, yield and its components (bulb and neck diameter, bulb fresh and dry weight and total yield as well as chemical content of onion bulb (T.S.S., Carbohydrate, nitrogen, phosphorus and potassium) gave the same previous trend. As regard to the effect of bio-fertilizers, the mixture of Nitrobeine combined with Phosphorene gave the highest values of all parameters, except neck diameter, followed by adding Nitrobeine as compared with using Phosphorene. As for the effect of the interaction between organic manures and bio-fertilizers, results indicated that application of poultry manure combined with the mixture of Nitrobeine and Phosphorene gave the best vegetative growth, bulbs yield and chemical bulb content