Sodium is indispensable for animals but not so for plants, so its acquisition is an important limitation for the survival of herbivorous animals. In this study, we aim to clarify the patterns of sodium availability with respect to the distance from the sea, main source for sodium in terrestrial ecosystems, and also the physiological response by Japanese macaques. We collected 150 live and dead leaf samples every ten meters along a transect in a lowland and highland forest of Yakushima, Kagoshima Prefecture, and Hakusan, Ishikawa Prefecture. The distances from the sea are 0-800 m, 5.0-5.9 km and ca 20 km, respectively. The sodium concentration was significantly higher in the lowland Yakushima than in the highland Yakushima and Hakusan. We examined concentration of aldosterone, a hormone enhancing re-absorbance of sodium in the kidney, in feces of wild Japanese macaques. In addition to the above three sites, we collected fresh fecal samples of Japanese macaques in Koshima, a small islet in Miyazaki Prefecture, where the wild Japanese macaques are provisioned on a beach. Aldosterone concentration was significantly lower in Koshima than the other three populations, indicating habitual contact with sea water alters the physiological sodium dynamics.