Human Interleukin-11 (hIL-11) is a multifunctional cytokine which modulates the proliferation, differentiation and maturation of hematopoietic cells. Recombinant hIL-11 is the first interleukin approved by Food and Drug Administration (FDA) to administer to patients with low platelet counts. In the previous paper, the authors reported the result of hlL-11 expression into the periplasm of Escherichia coli (E. coli) BL21 with PelB leader. However, the recombinant protein produced at very low level. Here, the authors show the result of hIL-11 expression in a fusion form with SUMO protein (Small Ubiquitin-like Modifier) in E. coli Rosetta 2. SUMO modulates protein structure and function by covanlently binding to the lysine side chains of the target proteins. A gene fragment coding for hIL-11 protein was optimized for codon adaption in E. coli. The 9ptimized gene was inserted into a SUMOpr03 vector and transformed into E. coli Rosetta 2 to express recombinant protein in fusion form with SUMO. The result showed that a strong band of 36 kDa derived from the' fusion protein SUMO-IL 11 was well expressed in the host cells. Importantly, the fusion protein was mainly present in the supernatant phase of the cell lysis.