Objective To investigate the role and underlying mechanism of spermidine(SPD)in intracerebral hemorrhage(ICH).Methods Male C57BL/6 mice were subjected to establish a collagenase-induced ICH model.The 108 mice were randomly divided into Sham group,ICH group and ICH+SPD group(intraperitoneal injection of 15 mg/kg SPD for 3 consecutive days after modeling),with 36 mice in each group.On the 3rd day after ICH,neurological deficits were evaluated using modified Garcia scoring and forelimb placing test;brain pathological damage was assessed with HE staining;activation of microglia/macrophages(Iba-1)and astrocytes(GFAP)was detected by immunofluorescence assay;expression of autophagy markers(Beclin-1,P62)and inflammatory factors(MMP-9,NLRP3,COX-2)was measured with Western blotting.In in vitro experiments,hemin was used to stimulate HT-22 cells to mimic ICH.The HT-22 cells were randomly divided into Control group,Hemin group,Hemin+SPD group,and Hemin+SPD+3-methyladenine(3-MA,an autophagy inhibitor)group(n=7).After 24 h of hemin treatment,cell viability was detected with CCK-8 assay,the expression of autophagy-related proteins(LC3-Ⅱ and P62)were detected with Western blotting,and oxidative stress was determined by measuring superoxide dismutase(SOD)activity and malondialdehyde(MDA)content.Results On day 3 post-ICH,SPD significantly reduced the area of brain damage(P<0.05),improved neurological recovery(P<0.05),activated autophagy with up-regulation of Beclin-1 while down-regulation of P62(P<0.05),suppressed the activation of microglia/macrophage and astrocytes(P<0.01),reduced the expression of MMP-9,NLRP3 and COX-2,and enhanced SOD activity and decreased MDA content(P<0.05)when compared with the ICH group.SPD increased the viability of HT-22 cells(P<0.05),improved SOD activity and reduced MDA content(P<0.01).Autophagy inhibitor 3-MA effectively blocked the down-regulation of LC3-Ⅱ and up-regulation of P62,and completely reversed above protective effects caused by SPD(P<0.05).Conclusion SPD activates autophagy after ICH and improves post-ICH brain injury by suppressing neuroinflammation and oxidative stress.