Abstract: Objective To observe the effect of ERK, P38 MAPK and JNK on the contractile response of vascular smooth muscle to norepinephrine (NE) after hypoxia, and explore its calcium sensitivity regulation mechanism of myosin light chain (MLC20) phosphorylation. Methods With hypoxia-treated vascular smooth muscle cell (VSMC) and hemorrhagic shock model of rats, the contractile response of VSMC to NE after hypoxia were observed by fluorometric method. At the same time, the MLC20 phosphorylation of superior mesenteric artery (SMA) in hemorrhagic shock rats was detected by Western blot, and the calcium sensitivityof SMA was assayed with isolated organ perfusion system. Results After hypoxia, the contractile response of VSMC to NE was significantly decreased. Meanwhile the level of MLC20 phosphorylation and calcium sensitivity of SMA after shock were decreased. Angiotensin II (AngII), with the effect of MAPK stimulation, could increase the contractile response of VSMC to NE after hypoxia, and increased the level of MLC20 phosphorylation and calcium sensitivity of SMA after shock. PD98059 (ERK inhibitor), SB203580 (P38 MAPK inhibitor) and SP600125 (JNK inhibitor) antagonized the effects of AngII-induced increase of the contractile response of VSMC after hypoxia. And ERK and P38 MAPK inhibitors also antagonized the effects of AngII-induced increased the level of MLC20 phosphorylation and calcium sensitivity of SMA after shock, while JNK inhibitor had no effect. Conclusions ERK, P38 MAPK and JNK were involved in the regulation of the contractile response of VSMC after hypoxia, and the mechanism of ERK and P38 MAPK was possibly through MLC20 phosphorylation dependent mechanism (calcium sensitivity regulation pathway), while JNK may be partially involved in regulating of the contractile response of VSMC by other mechanisms.