Injectable sustained-release pcDNA3-GRF (1-32) microspheres were prepared by double emulsion-in liquid evaporation process,using biodegrable poly lactic-co-glycolic acid as carrier. The enrapment efficiency, mean particle size, drug content thus prepared were 69%, 2.20 microm, 8% and 70% respectively. The result of transfection in vivo showed that after 30 days, accumulative increased body weights on the group injected with pcDNA3-GRF (1-32) microspheres was significantly higher than those group injected with naked plasmid (12.87%), plasmid-empty microspheres (19.72%) and saline (58.58%) respectively. PCR and RT-PCR showed that the expression level of GRF gene on the group injected with pcDNA3-GRF (1-32) microspheres was the highest. GRF gene released by microspheres was still detected after 30 days. In conclusion, pcDNA3-GRF (1-32) microspheres have a controlled release effect and GRF gene could be successfully transfected into muscle cells of mouse by microspheres with higher efficacy and stronger biological function.