This study aims to characterize the estrogen receptor (er) in sand goby (Pomatoschistus minutus) and determine the temporal effects of 17a-ethinyl estradiol (EE2) on era and vitellogenin (vtg) gene expression in males. Two partial cDNA sequences (era and erß1) are presented showing conserved structural features with ers of other species. Transcript levels for both ers were low in control fish but EE2 exposure (11 ng/L, for 29 days) increased both to a pattern similar to vitellogenic females. The relative expression of three vtg genes (vtga, vtgb and vtgc) along with era was determined in control and male fish exposed to EE2 (11 ng/L) at multiple time-points over 29 days. All four transcripts were significantly induced due to exposure and expression rose during the time course with distinct temporal patterns and vtga reached a substantially higher level at the end of the time course coinciding with rapid elevation in era expression.