Naproxen (NPX), one of the most widely used non-steroidal anti-inflammatory drugs (NSAIDs), has shown an increasing detection frequency in the marine environment in recent years. Due to its pseudo-persistence in aquatic systems, marine organisms may experience long-term low-dose exposure, potentially leading to adverse effects. In this study, marine medaka (Oryzias melastigma) was employed as the test organism to investigate the effects of cross-generational (F₁ generation and F₂ generation) continuous exposure to various NPX concentrations on early development and antioxidant systems. Embryos from two generations were exposed to 0, 0.1, 1, and 10 μg·L^-1 of NPX for 30 days, during which hatching rate, hatching time, heart rate, and larval mortality were measured and recorded. Antioxidant system indicators in embryos at 8 days post fertilization were also examined. The results demonstrated that even at environmentally relevant concentrations, NPX caused significant early developmental toxicity in marine medaka. Both generations exhibited marked decreases in hatching rate, consistent heart rate disturbances, and increased larval mortality with rising NPX concentrations. Notably, at 10 μg·L^-1, hatching time was prolonged by approximately 20% compared with the control group. Furthermore, NPX exposure triggered oxidative stress in marine medaka embryos, with F₂ embryos generally showing more severe oxidative damage than F₁. Nevertheless, the F₂ generation displayed a certain adaptive response, resulting in a lower mortality rate compared to F₁ generation.