Two kinds of ectopic expression of porcine growth hormone-releasing hormone (GHRH) plasmids, ppG-A53f-H6-GHRH (ppG-H6) and ppG-A53f-H4-GHRH (ppG-H4), were constructed by using a myogenic expression vector which has α-actin expression elements. After the animal was injected in the muscle with the two plasmids, the body-weight data at the 0 / 3/ 7/ 11/ 14/ 17/ 20/ 24/ 27/ 31/ 34/ 38/ 41st days were collected. Rat plasma from blood collected at the 20/ 27/ 34/ 41st days was made and growth hormone (GH) levels were determined by radio immunoassay (RIA). The results indicated that ppG-H6 and ppG-H4 do enhance the rat growth compared to the control, with the ppG-H6 treated group showing a more effective response. Compared with the control group, at the 34th day after injection, the weight gain of the ppG-H6 group was significant ((200.57±3.99) g vs (185.85±9.45) g, P < 0.05). Furthermore, the GH maintains on a stable level in group ppG-H6 and ppG-H4 compare to control by the end of experiment, which support that the injection of ppG-H6 and ppG-H4 plasmids caused the body-weight of rat increasing. The results imply that injection of ectopic expression of porcine growth hormone-releasing hormone (GHRH) plasmids is a possible way to enhancing animal growth.