The objectives of the present study were to investigate the effects of oral administration of estradiol-17β (E₂) on luteinizing hormone (LH) in plasma, aromatase activity in gonad, and sex change in the fingerlings of protandrous black porgy, Acanthopagus schlegeli Bleeker. The expression of estrogen receptor (ER) and androgen receptor (AR) transcripts in gonad was also analyzed. Undifferentiated (2-mo-old) black porgy were divided into two groups, one fed a control diet and the other a diet mixed with E₂ (6.0 mg/kg feed) for 5 mo. Fish treated with E₂ for 3 mo showed complete suppression of spermatogenesis and spermiation and induced sex change with primary oocytes. Aromatase activity in forebrain and midbrain was increased in the control in December–March (during the spawning season). E₂ stimulated aromatase activity in the brain. Higher gonadal aromatase activity in concordance with elevated levels of plasma LH was observed in the E₂ group compared with the control. After 2-mo of E₂ termination, regressed testicular tissue recovered and controlled females gradually reversed back to functional males in January and March. Plasma LH levels were higher in the E₂-terminated group during the period of reversible sex change (from a controlled female to male) compared with the control. The expression of ER and AR transcripts was closely related to the development of testis and ovary. The data showed that E₂ induced a reversible sex change with high plasma LH. Increase of gonadal aromatase and decrease of ER/AR were associated with controlled sex change. Plasma LH levels were correlated with the conversion from a controlled female to male in black porgy.