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To functionally express the recombinant mouse insulin-like growth factor-I (rtmIGF-I) in Lactococcus lactis NZ9000 with a food-grade vector.The rtmIGF-I encoding sequence was inserted into secreted food-grade vector pLEB688 and transformed into L. lactis NZ9000. The expression of the recombinant protein rtmIGF-I was confirmed by tricine-SDS-PAGE analysis and Western blot. The concentration of this recombinant protein was 3 mg l−1 in the medium fraction. Further experiment demonstrated that the recombinant protein was biologically active and promoted NIH3T3 cell proliferation in a concentration-dependent manner.The rtmIGF-I was expressed in L. lactis and located into the medium fraction. The optimal final concentration which could promote NIH3T3 cell proliferation after incubation was 100 ng ml−1.The rtmIGF-I was functionally expressed in L. lactis NZ9000 with a food-grade vector. Thus, the recombinant L. lactis NZ9000 could act as a host for the production of rtmIGF-I for further study. The recombinant strain could serve as an IGF-I delivery system.