Abstract: The yak (Bos grunniens) is an important grazing livestock in Western of China. In this study, the full length of yIFN-a1 gene was cloned then the recombinant yIFN-a1 was expressed in yeast expression system. In vitro bioactivity of IFN-α1 was determined by inhabition infection BHK cell against Vesicular Stomatitis Virus (VSV). The results showed that cDNA contains an Open Reading Frame (ORF) of 570 base pairs encoding a protein of 189 amino acid (aa) precursor with a signal peptide of 23 aa. The homology of the yIFN-a1 was up to 65.3~94.4% with other species at the amino acid levels. The recombinant yIFN-a1 was recognized in Western blot by mAb against human IFN-α1. The activity unit of the purified recombinant yIFN- a1 protein was 1.16×105 IU mg-1 by against Vesicular Stomatitis Virus (VSV) antiviral assay in vitro. This made a basis for the development of anti-virus medicine of yak in the future.