Selenium (Se) is naturally found in marine environments. At low concentrations, it causes both low hatching and emergence success in oviparous animals. The objective of this study was to compare serum Se concentrations between wild and captive hawksbill turtles, Eretmochelys imbricata, and investigate changes in Se concentration in turtles during captivity. Serum Se concentration was measured in 45 wild and captive hawksbill turtles. The mean Se concentrations in the serum of wild hawksbill turtles (x̄ ±SD=0.98±0.57 µg/g, n=16, range=0.18–2.61 µg/g) were significantly higher compared to those in captivity (x̄ ±SD=0.30±0.10, n=29, range=0.05–0.42). Serum Se concentrations remained almost constant irrespective of the rearing period and it began to decrease 1–2 years after rearing, which may result in low emergence success rates under managed care.