The suppressor of cytokine signaling 1 (SOCS1) is a crucial regulator in the immune systems of mammals, which functions classically as a negatively regulator in the IFN signaling pathways. However, data on functional characterization of SOCS1 in lower vertebrates is limited. In this study, we identified and characterized the full-length SOCS1a gene of miiuy croaker (Miichthys miiuy). The sequence analysis results showed that miiuy croaker SOCS1a (mmSOCS1a) shared some conserved motifs with other vertebrates. To further study the function of fish SOCS1, we identified mmSOCS1a and determined its potential ability to perceive poly(I:C) stimulation. Induction experiments with poly(I:C) indicated the significant expression levels of mmSOCS1a in liver and kidney. In addition, mmSOCS1a could inhibit poly(I:C)-induced or IFNs-induced ISRE reporter gene activation. In a word, we systematically and comprehensively analyzed evolution and function of mmSOCS1a, which will provide the basis for future research on fish SOCS family.