This study investigated the estrogenicity of 4-nonylphenol (NP) and diethylstilbestrol (DES) in vitro during oocyte maturation in the marine fish, Tridentiger obscurus, using steroid hormone assays and GVBD assay. Vitellogenic (0.53mm diameter) and fully vitellogenic (0.75mm diameter) oocytes were in vitro exposed to NP (0.045 453.82 nM and DES (0.037 372.62 nM). In vitellogenic oocytes, 45.38 and 453.82nM NP and 3.73 372.62nM DES increas the estradiol-$17{eta}$ (E2)/testosterone (T) ratio. In fully vitellogenic oocytes, 0.45, 45.38 and 453.82nM NP and 3.73nM DES increased E2/T. In the GVBD assay, 0.45 and 4.54nM NP and 0.037, 3.73 and 37.26nM DES inhibited GVBD. These results suggest that NP and DES have estrogen-agonistic effects in oocyte maturation in T. obscurus. In addition, NP and DES have different sensitivity according to the oocyte developmental stage, and the estrogenagonistic effects of DES were greater than were those of NP.