This study investigates the effects of environmental concentrations of 17α-ethinylestradiol (EE2), a synthetic estrogen and endocrine-disrupting chemical, on the osmoregulatory functions of yellowfin seabream (Acanthopagrus latus). Endocrine disruptors like EE2 interfere with hormonal balance in aquatic organisms, potentially affecting physiological processes such as growth, reproduction, and osmoregulation. To assess the potential impact of EE2, a semi-static experimental setup was used in which yellowfin seabreams were exposed to a concentration of 10 ng/L EE2 over two weeks. Calcium carbonate (CaCO₃) excretion rates were measured as a primary indicator of osmoregulatory function. The results showed no significant changes in CaCO₃ excretion rates, suggesting that short-term exposure to this concentration does not induce measurable osmoregulatory disruptions in this species. However, given the bioaccumulative nature of EE2 and its persistence in aquatic environments, further research is needed to evaluate the long-term effects and potential risks associated with prolonged exposure and higher concentrations. Understanding these impacts is crucial for assessing the ecological risks of pharmaceutical contaminants in marine environments and developing appropriate regulatory measures to mitigate potential harm to marine biodiversity.