Abstract: The cDNA full length sequence of STAT (HsSTAT, GenBank ID: KY123702) was obtained from Hyriopsis schlegelii first time using the TACE-PCR technique. The full length of HsSTAT is 2752 bp. The lengths of the 5′-untranslated region, 3′-untranslated region, and ORF region are 121, 264 and 2367 bp, respectively, and it encoded 788 amino acids. The protein domain consists of four classical conservative function domains, including STAT_int, STAT_alpha, STAT_bind and SH2. Valine possesses the highest percentage of 12.9% in the sequence, and lysine has the lowest percentage of 0.5%. The utilization frequency analysis of amino acid at the conservative locus showed that only tryptophan reached 100% utilization. The secondary structure of HsSTAT shows that the percentages of α-helix, β-folding, extension chain, random coil were 46.83%, 8.5%, 15.36% and 29.31%, respectively. Furthermore, the third structure analysis give a prediction of four classical domains. In addition, the hydrophobicity analysis show that the HsSTAT protein is hydrophilic with an index of –0.531. 1 palmitoylation modification site, 3 small ubiquitin-related modification sequences, and 22 phosphorylation sites were predicted. Phylogenetic tree analysis showed that HsSTAT is clustered with Biomphalaria glabrata STAT5B and Haliotis discus discus STAT5. Subcellular localization results indicate that HsSTAT is located in the cytoplasm of hemocytes. Fluorescence in situ hybridization shows that the expression of HsSTAT is mainly in nucleus. The results of qPCR show that HsSTAT is expressed in all tissues, among which it has the highest expression in the hepatopancreas and the lowest in hemocytes. The proliferation results show that HsSTAT helps promote the proliferation of SMCC-7721 cells.