Waste onion leaves were found to possess flavor, aroma and bioactive components similar to that of onion bulb which are useful in various food applications making it a potential alternative spice.Although drying is known as a preservation technique for herbs such as onions, it is often accompanied with loss of volatiles and bioactive compounds. In this study, the changes in bioactive compounds of waste onion leaves in terms of total phenolic content (TPC) and total flavonoid content (TFC) as well as flavor and aroma components such as sulfur-containing compounds using various dehydration techniques (sun drying, conventional drying, freeze drying and vacuum drying) were evaluated. Effects of drying parameters such as temperature, time, vacuum pressure and blanching on preservation of bioactive compounds in waste onion leaves were also investigated. From these results, the type of drying method can significantly affect the bioactive components, as well as the flavor and aroma of dried onion leaves.