The biological activity of androgens is mediated by the nuclear androgen receptor (nAR) in vertebrates. nAR is a ligand-regulated transcriptional factor, which belongs to the nuclear receptor superfamily. nAR has been characterized from mammals to teleosts. The nAR subtype is found to exist in two different isoforms in several fish species due to a teleost specific gene duplication event. These subtypes of nAR form two distinct molecular clusters and display different tissue distributions and expression patterns during embryogenesis and gonad development. Recently, increasing evidence has shown the nongenomic or cell surface receptor (the membrane androgen receptor, mAR)-mediated actions of androgen. Here we review the gene structure; molecular and biological characteristics; tissue distribution; and ligand-binding features of nAR . Furthermore, we also review the characteristics, distribution and relationship of mAR with regards to the reproductive cycle in teleost fish.