Human thrombopoietin (TPO) has been successfully overexpressed in Escherichia coli, with an expression level of about 12% of total cellular protein. The full-length TPO gene was subcloned into the prokaryotic expression vector pKK233-2 under the control of the inducible tac promoter. The recombinant protein was produced mainly in the form of inclusion body. By efficient renaturation and one-step purification, the recombinant protein was purified to homogeneity. The specific activity and yield of recombinant TPO can reach 2 x 10(4) units/mg and 2 mg/g of wet E. coli cells respectively.