The chemical properties of yellow and red onion were investigated and analyzed to provide basic data for functional food materialization and processing. The moisture and nitrogen free extract contents of yellow and red onion were 92.80%, 5.13% and 92.47%, 5.59%, respectively. Mineral components of yellow and red onion were rich in K (123.64 and 114.41 mg%), Na (34.09 and 33.57 mg%) and P (27.04 and 20.56 mg%). The major free sugar of yellow onion were glucose (744.2 mg%) and fructose (705.9 mg%). Whereas major free sugar of red onion were sucrose (692.8 mg%) and fructose (517.3 mg%). Glutamic acid, phenylalanine and aspartic acid in yellow and red onion were major amino acids. Abundant free amino acids in yellow onion were hydroxy-L-proline (27.34 mg%), L-serine (27.34 mg%) and L-arginine (26.25 mg%). Abundant free amino acids in red onion were L-glutamic acid (16.35 mg%), ammonium chloride (15.22 mg%) and L-serine (10.93 mg%). Ascorbic acid contents are higher in red onion (28.34 mg%) than in yellow onion (19.20 mg%). Quercetin and total polyphenol of yellow and red onion were 15.24 mg%, 5.70 mg% and 0.319 mg/g and 0.248 mg/g, respectively.