Periplasmic expression of recombinant proteins ensures the production of biologically active proteins in a correctly folded state with several key advantages . This research focused on the in-frame cloning of rhIL-15 in pET-20 (+) vector with pelB-leader sequence to direct the protein to the bacterial periplasm . The target construct periplasmic expression was evaluated in four strains, BL21 (DE3), BL21 (DE3) pLysS, Rosetta 2 (DE3) and Rosetta-gami 2 (DE3). Soluble periplasmic expression of IL-15 was highest in Rosetta-gami 2 (DE3) followed by Rossetta 2 (DE3) whereas negligible expression was observed with rest of two expression host . Best expression clone was selected for purification by dye ligand affinity chromatography . Purified rhIL-15 was characterized by SDS-PAGE, Western blotting and SEC-HPLC . This is the first report of functional recombinant human interleukin-15 being expressed and purified with yield of 120 mg/L in the periplasmic space of E. coli.