Onion (Allium cepa L.) is one of the major vegetable crops cultivated worldwide. Since many onion cultivars are suitable for long-term storage, the summer crop is stored over-winter and supplied to the market over a year. For long term storage, conditions are optimized that are antagonistic for pathogens and favorable for the maintenance of bulb dormancy to delay sprouting, rooting and spoilage. It is imperative to understand the changes in chemical composition of onion during storage and whether these changes can be corroborated to more efficient storage under ambient and/or different storage temperatures. In this study, onion bulbs of a popular Korean onion cultivar 'Sunpower' were stored at different ambient conditions under dark and light conditions. Analysis of chemical composition of stored onion bulbs revealed notable fluctuations in the flavonol and sugar contents while, the amino acid content remained relatively unchanged till the onset of inner sprouting.