Green sea turtle (Chelonia mydas) eggs were incubated at different temperatures. Hatchling sex was determined by the standard histological examination,and sex hormone test in the amniotic fluid and plasma. The histological findings of this study indicated that the testis showed thin cortex and more medullary cavity, and conspicuous medullary cords surrounded by stromal tissue,while the ovary showed thick cortex and less medullary cavity. Different sizes of immature oocytes were observed in the stroma of ovary. The sex hormone test indicated that the ratio of estradiol (E₂) and testosterone (T) could be used to determine the sex: when E₂∶T<1.5,the hatchlings were males (♂); when E₂ ∶ T> 1.5,the hatchlings are females (♀). Pivotal temperatures (PT) for sex determination in Sea Turtle Bay of China ranged from 29.4℃ to 29.5℃ ,with an approximate 1∶1 sex ratio.