Abstract: The complete open reading frame （ORF）of interleukin-15 gene was amplified from Rongchang porcine peripheral blood lymphocyte stimulated by ConA, which includes 489bp and encodes 162aa. Sequence analysis indicated that the nucleotide shared 99.4% homology with two other porcine IL-15 genes reported previously. Phylogenetic analysis showed that the evolution relationship is comparatively close to the human and mammal IL-15 gene while it is fairly away from poultry. The gene encoding mature IL-15 protein was amplified by PCR from the recombinant plasmid containing IL-15, which includes 345 bp in all. Then it was cloned directionaly into prokaryotic expression vector pET-32a(+) and the fusion expression was induced in E.coli BL21. SDS-PAGE demonstrated that the fusion protein expressed in form of inclusion body is approximately 34 ku, the product of expression account 38.7% of the total bacterium proteins. Western-blotting analysis indicated that there is a specific electrophoresis strip at the place where the relative molecular mass is about 34 ku. A 356 bp specific fragment strip was observed by detection after the recombinant bacteria was transcribed. After the protein was purified roughly and renatured, MTT essay confirmed that it can enhance lymphocyte proliferation obviously. Rongchang porcine interleukin15 mature peptide was expressed successfully in vitro and it possesses certain biological activities.