Two field experiments were carried out at Bahteem farm, Agricultural Research Station, Agricultural Research Center, Giza, in two successive winter seasons during 2005/2006 and 2006/2007 on onion crop. The objective of these experiments are to study the effect of micronutrients mixture (Zn 1.5%, Mn 2%, Fe 3%, Cu 1%,MgO 4% and B 0.5%) applied at two concentrations of 250 and 500g fed^-1 and free amino acids mixture (29.7% w/v) also at two concentrations of 1.5 and 3.00 L fed-1 on onion plant growth, dry matter yield, its yield components and chemical characteristics (bulb total soluble solids, bulb pH and bulb NPK contents) of onion variety Giza 20. Both micronutrients and free amino acids mixture were sprayed on onion plants at two periods of 60 and 75 days from transplanting. Results indicate that foliar application for both amino acids and micronutrients together on onion plants led to an increase in onion yield and its components, total soluble solids and NPK bulb contents. However, the foliar spray effect of both amino acids (1.5 L fed^-1) and micronutrients (250 g fed^-1) on all the onion plant tested parameters was superior than those recorded due to the use of both amino acids (3 L fed^-1) and micronutrients (500 g fed^-1) without significant difference. In conclusion, the foliar spray of both amino acids and micronutrients together on onion plants could improve the onion yield and its components.