Factors which affect the content of flavonoids in Kijitsu were studied. Flavonoids in immature citrus fruit decomposed gradually by standing after divided horizontally in two parts. About 90% of flavonoids were retained by use of hot air drying of fresh samples. The content of flavonoids in Kijitsu decreased to about 60% by standing one year. Flavonoid contents decreased corresponding with an increase in diameter of Kijitsu. There is no wide difference between Hassaku and other Citrus fruits in their essential oils determined by gas chromatography-mass spectrometry. It was concluded that C. hassaku might be used for the material for Kijitsu.