Quantitative changes in various terpene hydrocarbons (α-pinene [1], β-pinene [2], myrcene [3], d-limonene [4], γ-terpinene [5]) were studied in Satsuma Mandarin juice during storage. Compound [1] yielded α-terpineol [6] and β-terpineol [7] as hydration products. Hydration of [2] yielded [6] as the main product and fenchyl alcohol [8] as the minor product. Terpinen-4-ol [9], [6] and [7] were produced from [4]. Compounds [3] and [5] were quite stable in the juice. Isomerization of terpene hydrocarbons [1_??_5] was also observed. Further-more, the precursors and formation mechanisms of the off-flavored compounds [6, 7, 8] of the juice were suggested.