Objective：To investgate effects of acupoints electroacupuncture on the expression of matrix metalloproteinase-9 （MMP-9）in the mandibular protrusion of rats. Methods：Totally 60 male SD rats were randomly divided into 4 blank control groups，4 con－ditional control groups and 4 experimental groups（n=5，respectively）. Rats were sacrificed on 3，7，14，28 d after experimental mandi-bular protrusion. Immunohistochemistry and real-time PCR methods were used to detect expressions of MMP-9 in growing rats’ mas－ticatory muscle. Results：Compared with those in blank control groups，MMP-9 expressions were significantly increased in conditional control group on 7，14 d，with statistical differences（P<0.05）；MMP-9 expressions were significantly increased in experimental group on 3，7，14 d，with statistical differences（P<0.05）. Compared with those in conditional control group，MMP-9 expressions were signifi－cantly increased in experimental group on 3，7 d，with statistical differences（P<0.05）；there was no significant difference between the two groups on 14 d（P>0.05）；MMP-9 expressions were significantly decreased in experimental group on 21 d，with statistical differ－ences（P<0.05）. Conclusions：Electric acupuncture can up regulate the expression of MMP-9 in rats masticatory muscle after func－tional mandibular protrusion，which may improve the treatment effect of functional appliance.