Abstract: Guanine nucleotide binding protein (G protein), composed of α, β and γ subunits, is an important signal transduction molecule in cAMP signaling pathway by directly regulating ion channels and activating second messengers. To investigate the function of the Gs in Fenneropenaeus chinensis under acute low salt stress, the full-length cDNA of Gs in Fenneropenaeus chinensis, named FcGs, was cloned by rapid amplification of cDNA ends (RACE), and then examined its response under acute low salt stress. The full length of the FcGs gene cDNA sequences consists of 1692 base pairs (bp), including a 1140 bp open reading frame (ORF) which encodes a 379-amino acid peptide with four transmembrane domains. Homology and phylogenetic analysis showed that deduced FcGs amnio acid sequence is highly conservative, with the highest amnio acid sequence identity (99%) with Litopenaeus vannamei, and a high amnio acid sequence identity (97%) with Marsupenaeus japonicus. Results of RT-qPCR showed that FcGs gene expressed in all tissues of Fenneropenaeus chinensis, with the highest expression level in gill, followed by hepatopancreas. Acute low salt stress upregulated FcGs, which is consistent with increased Dopamine (DA) content, Gs content, adenosine cyclase (AC) activity, cAMP content, protein kinase A (PKA) activity and Na⁺-K⁺-ATPase activity in cAMP signaling pathway of Fenneropenaeus chinensis. RNA interference (RNAi) of FcGs increased the mortality of Fenneropenaeus chinensis by the acute low salt stress. This study shows that FcGs gene and its cAMP signaling pathway play an important role in the osmotic regulation of Fenneropenaeus chinensis by regulating the activity of Na⁺-K⁺-ATPase.