TNFSF11, also known as RANKL, is a member of the tumor necrosis factor (TNF) cytokine family which is a ligand for osteoprotegerin and functions as a key factor for osteoclast differentiation and activation. TNFSF11 also has a function in the immune system, where it is expressed by T helper cells and is thought to be involved in dendritic cell maturation. TNFSF11 is important in bone metabolism. This natural and necessary surface-bound molecule (also known as CD254) found on osteoblasts serves to activate osteoclasts, which are the cells involved in bone resorption. Recombinant human TNFSF11 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.