The β-thymosin (Tβ) proteins participate in numerous biological processes， such as cell proliferation and differentiation， anti-inflammatory and antimicrobial mechanism. To date， Tβ proteins have been well studied in vertebrates， especially mammals. While limited Tβ or Tβ-like proteins have been reported in invertebrates. Moreover， rare information of Tβ or Tβ-like proteins is available in scallop species yet. In the present study， two Tβ homologues， AiTβ and CfTβ， were identified and characterized from two scallop species bay scallop Argopecten irradians and Zhikong scallop Chlamys farreri. They were both 41 amino acid peptide and contained one THY domain， a highly conserved actin-binding motif and two conserved helix forming regions. Tissue distribution and expression profiles of their mRNA transcripts were roughly similar yet different in detail， while their recombinant proteins exhibited different immunomodulation activity on the downstream immune parameters. These results collectively indicated that the function of Tβ family in scallop were functionally differentiated.