Abstract: The enzyme aromatase P-450（P450arom） catalyzes the conversion of androgen to oestrogen. A cDNA encoding P450arom was derived from yellow catfish （Pelteobagrus fulvidraco） brain, using RT-PCR and RACE. The cDNA was 2080 bp with 25 bp 5′ UTR, 555 bp 3′ UTR（ excluding poly（A） ） and 1500 bp ORF, which encodes 500 amino acids and has a predicted mol wt of,56 kDa. The yellow catfish brain-derived P450arom shares above 70% sequence identity with brain-derived aromatases of other fish species, but only about 60% with ovarian aromatases of other fishes, about 50% with human placenta and chicken ovarian aromatases. But the percentage of identity/similarity was higher in the regions of high homology, including the Ⅰ-helix, an aromatase-specific conserved region Ⅱ, and the heme-binding region Ⅲ, their homology being 823% - 96%, 78% - 86% and 85% - 100% respectively. Phylogenetic analysis of the P4.50arom gene family indicated the yellow catfish brain-derived P450arom was clustered with other fishes brain-derived P450arom, and is the closest with channel catfish. This result is consistent with the result of traditional classification. The fluorescent real time quantity RT-PCR analysis revealed HP450arom B is expressed in fore-brain , hypothermia, pituitary, ovary and testis, but is high in brain and low in gonad. There is no expression in liver. There is no significant difference between male fish and female fish brain.