Abstract: To understand the secretory expression of heterologous protein in Bacillus subtilis, especially of those from eucaryotes, also to reveal the role of propeptide, two recombinant plasmids containing TPO gene were cloned in Bacillus subtilis with or without propeptide, named Pro-TPO, SP-TPO respectively. PCR production fragment SP containing signal peptide was ligated with TPO and vector. The recombinant plasmid was transformed into DB403 and a positive clone DB403(SP-TPO) was obtained. Another recombinant was available at the same time with the regulatory sequence Pro containing signal peptide and propeptide, named DB403(Pro-TPO). The secretion of TPO of the three recombinants can be valued by means of ELISA and Western blot. DB403(Pro-TPO) was shown to have the ability of secreting TPO, however DB403(SP-TPO) was found no secretion. DB403(Pro-TPO) was administrated peritoneally to Babl/c mice and got the number of platelet increased by 84.2%(self control) and 99.7%(saline control). The results implied that TPO is expressed with native activity and propeptide is essential for the secretion of TPO.