In Tokushima Prefecture, sudachi (Citrus sudachi Hort. ex Shirai) is a major productive citrus fruit, and there is a dietary habit of putting sudachi juice on shirasuboshi (boiled and semi-dried whitebait), which is a food rich in calcium. Therefore we examined the effects of citrus fruit juices on solubilization of calcium from shirasuboshi. About 50% of total calcium was solubilized into the aqueous phase after addition of citrus fruit juices including sudachi, lemon (Citrus limon Burm. f.) and yuzu (Citrus yunos Sieb. ex Tanaka) to Shirasuboshi, and then accumulation of the calcium in the aqueous phase was observed upon standing for up to 70 min. Calcium solubilization from shirasuboshi was also observed when using sudachi juice adjusted to neutral or alkaline pH. Citric acid was found to be the major organic acid in sudachi juice at a concentration of 60mg/ml, which solubilized calcium from shirasuboshi, suggesting that citric acid in sudachi juice may play an important role in the solubilization phenomenon. Shirasuboshi mixed with sudachi juice was treated with pepsin followed by pancreatin to simulate the gastrointestinal digestion process, which resulted in almost 100% of total calcium in shirasuboshi being solubilized, compared with only 50-60% using vinegar or water instead of sudachi juice. These results suggest that the dietary habit of putting sudachi juice on shirasuboshi increases calcium absorption in vivo.