Abstract: Aquaporin, a superfamily of internal membrane proteins that mediate transmembrane transport of water molecules, plays an important role in osmotic adjustment. AQP1a gene was obtained in order to study the role of AQP1a in osmoregulation of Trachinotus ovatus under acute salinity stress. The sequence of AQP1a gene was 1 078 bp with an open reading frame of 786 bp encoding 261 amino acids. The structural analysis shows that it has the structural characteristics of MIP family-specific sequence (HINPAVTLG) and two asparagine-proline-alanine (NPA) motifs. The qRT-PCR results show that AQP1a was distributed in the 11 tested tissues, highest in gonads and then in gill, intestine and liver, lowest in muscle. Under acute salinity stress, after being transfered to fresh water, the expression of AQP1a in gill increased at 4^th hour, while there was no significant change in the expression in kidney and intestine. After being transfered to 10‰ and 20‰ salinity seawater, the expression of AQP1a in gill increased significantly at 2^nd and 4^th hour, and then decreased gradually. When being transferred to 10‰ salinity seawater, the expression of AQP1a in intestine increased. In kidney, the expression of AQP1a first increased and then decreased. When being transferred to 20‰ salinity seawater, the expression of AQP1a in intestine only increased significantly at 4^th, 8^th and 48^th hour. In kidney, the expression of AQP1a reached the maximum at 12^th hour. In 40‰ salinity seawater, the expression of AQP1a in gill decreased significantly. On the contrary, the expression of AQP1a in kidney and intestine were significantly up-regulated. The results reveal that the specificity of AQP1a functions in different tissues and plays an important role in T.ovatus salinity adaptation.