Abstract: Crassostrea hongkongensis is one of the pillar industries of mariculture in the coastal areas of South China. In recent years, with the continuous expansion of the scale of cultivation, the destruction of the breeding environment and the frequent occurrence of diseases, the large-scale death of C. hongkongensis has occurred, which seriously restricts the healthy and sustainable development of C. hongkongensis. Therefore, it is very important and urgent to carry out immune research for the healthy and sustainable development of C. hongkongensis. In this study, the immune function of T-cell acute lymphocytic leukemia (tal) in C. hongkongensis was studied, RACE technique was used to clone the full-length cDNA sequence of the (T-cell acute lymphocytic leukemia) tal gene of C. hongkongensis, named Chtal. The open reading frame (ORF) is 660 bp, encoding 219 amino acids, with the relative molecular weight of 25.11 ku. Multiple sequence alignment and phylogenetic tree results showed that the Chtal gene had high homology with C. gigas, C. virginica and Aplysia californica, which proves that it is a member of the tal family of mollusks. Fluorescence quantitative PCR results showed that Chtal was the most highly expressed in haemolytic lymphocytes of oyster in C. hongkongensis, followed by heart, gill and digestive gland, suggesting its function in lymphogenesis. After the stimulation of Vibrio alginolyticus and Staphylococcus haemolyticus, the expression levels of Chtal were significantly up-regulated, reaching the highest levels at 24 and 12 h, respectively, and the expression of the gene gradually decreased with time. The results of subcellular localization showed that Chtal was expressed in the nucleus. In vivo injection of recombinant tal can significantly increase the number of hemocytes. Edu proliferation assay further confirmed that Chtal could promote the regeneration of hemocytes in C. hongkongensis. In summary, this study revealed that Chtal was involved in hemocytes regeneration, providing a basis for further research on the function of this gene in immune response of oysters.