To characterize mineral nutritional features of plants, leaf samples from 39 plant species (n = 4 to 45) were collected from Ogasawara Islands, and N, P, K, Ca, and Mg contents were analyzed. Average Mg contents for 39 species were in the range between 0.14 and 1.26%, with 19 species having higher values than 0.4%, which is twice of general Mg content of 0.2%. This would be caused by high Mg contents of bed rock specifically found in these islands. In the leaves of Asplenium nidus, Ficus boninsimae, Morus australis, Hibiscus glaber, and Emilia sonchifolia, Ca and K contents were also high as well as Mg contents, resulting in ordinary Ca/Mg and Mg/K values. These species would preserve their homeostasis by increasing Ca and K contents for adapting to the high Mg environments. Other species having high Mg contents may have different adaptation mechanisms to the high Mg environments. On the other hand, N and P contents of most species were in the general range of 0.75 to 3.0% and 0.1 to 0.4%, respectively, and only 2 species showed higher contents than the general range for each element. These results indicate that many plants on Ogasawara Islands would be characterized by their adaptation to the high Mg environments.