Abstract: Objective To study the effect of rosuvastatin on blood pressure,vascular structure and vasodilatation function of third grade branch mesenteric in spontaneously hypertensive rats（SHR）. Methods Thirty-two male SHR at 12 weeks old were randomly divided into 2groups:rosuvastatinSHR-R,n=16,10mg/（kg·d）and untreated controls（SHR,n=16）. Age and weight-matched WKY rats served as controls（WKY,n=16）. The control rats were administrated equivalent distilled water. Systolic blood pressure（SBP）was determined by tailcuff method before treatment,4and 8weeks after treatment. The wall-to-lumen area ratios（W/L）,the ratios of wall thickness（WT）to lumen radius（LR）of third grade branch mesenteric arteries were assessed morphometrically.Endothelium-dependent relaxation（EDdR）,endothelium-independent relaxation（EDiR）were measured by PowerLab biological signal analytical system. Results SBP in SHRs was remarkably higher than that in WKY from 12 to 20weeks of age（P＜0.01）. SBP in SHR-R group was significantly lower than that in untreated rats after 4,8weeks of treatmentSBP in 4 weeks:SHR-R（180.0±14.6）vs SHR（200.3±13.9）mm Hg;8 weeks:SHR-R（180.1±13.5）vs SHR（189.9±10.1）mm Hg,both P＜0.01. W/L and WT/LR in SHR-R showed a mild tendency of descend while exited no statistical difference after 4 weeks treatment（P＞0.05）. W/L SHR-R0.51±0.21 vs SHR 1.82±0.96,P＜0.01and WT/LR SHR-R 0.23±0.04 vs SHR 0.53±0.29,P＜0.01of third grade branch mesenteric arteries in treated rats were markedly lower than that of untreated SHR after 8weeks treatment,of which WT/LR in R-SHR was similar to the level as that of WKY（P＞0.05）. EDdR and EDiR of third grade branch mesenteric arteries were reduced in untreated SHR. After 4weeks treatment,EDdR of third grade branch mesenteric arteries was increasedEmax:SHR-R（47.41±10.74）% vs SHR（29.10±7.35）%,WKY（83.85±5.17）%;pD2:SHR-R 6.39±0.90 vs SHR 5.96±0.58,WKY 8.34±0.21,both P＜0.01. EDiR was also enhanced Emax:SHR-R（75.23±20.10）% vs SHR（46.13±11.45）%,WKY（96.28±2.68）%;pD2:SHR-R 6.72±0.44 vs SHR 5.56±0.23,WKY 7.84±0.13,both P＜0.01. After 8week treatment,enhancement of EDdR and EDiR was not statistically significant compared to that after 4 week treatment.Conclusion Rosuvastatin may mildly lower blood pressure,attenuate remodeling of third grade branch mesenteric arteries after 4weeks treatment,and ameliorate vasodilatation function after 8weeks treatment in SHR. The increase of vasodilatation function was prior to improvement of vascular structure.