Talpha1 (thymosin alpha 1) is important in treating immunodeficiency and other diseases. In order to study the feasibility of expressing Talpha1 in plants, as the first attempt, we designed and synthesized the Talpha1 gene according to the plant codon usage preference and constructed the 4xTalpha1 concatemer (four copies of a DNA sequence arranged end-to-end in tandem). The latter was inserted into Escherichia coli expression vector pQE30, resulting in a recombinant plasmid that was subsequently transformed into E. coli M15. The 4xTalpha1 concatemer protein was successfully expressed in E. coli in a soluble form. The expressed protein was purified and its bioactivity was analysed by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. Preliminary results showed that the 4xTalpha1 concatemer protein could stimulate the mice spleen lymphocyte proliferation. This is the first report on the expression of 4xTalpha1 concatemer that was synthesized according to plant codon usage preference in an E. coli expression system. The present study provides the basis for expressing the synthesized active Talpha1 gene in plants in the future.