Finger citron [Citrus medica L. var. Sarcodactylis Hort, Rutaceae] (FC) fruits, widely cultivated in Japan, the southern provinces of China and Taiwan, are commonly used as functional vegetables and preserved as sweetmeats. Previously we identified the major compounds in essential oils (% in EO) of FC fruits to be d-limonene (51.24), gamma-terpenene (33.71), alpha-pinene (3.40), and beta-pinene (2.88). Documented evidence on its insulin secretion characteristics is still lacking. In parallel to compositional analysis, we performed in vivo the safety, hypoglycemic, and antidiabetic tests in Sprague-Dawley-SPF rats and Wistar DIO rats respectively. By kinetic analysis on the hypoglycemic patterns of the intraperitoneal glucose tolerance (IPGTT) and the insulin-glucose tolerance tests (IGTT), its insulin secretagogue effect was confirmed. In conclusion, FC fruits that concomitantly possess insulin secretagogue and slimming effects would be very beneficial to type 2 diabetes mellitus patients.