Objective To study the changes of magnetic resonance diffusion weighted imaging(DWI) in acute cerebral ischemia and reperfusion injury. Methods Adult healthy NewZeadand rabbits(103 cases) were used to established middle cerebral ischemia and reperfusion (MCAO/R) model by intraluminal thread technique, and 58 successful models were randomly divided into permanent ischemic group(30 cases) which further divided into ischemic 1 h,3 h,6 h,12 h,24 h,48 h groups consisting 5 cases and ischemic reperfusion group 28 cases which further divided into reperfusion 0h,2h,5h,11h,23h,47h groups consisting 5,5,5,4,5,4 cases respectively.Another 10 rabbits were regarded as ischemic contrast(5 cases) and reperfusion contrast(5 cases).The changes of hyper-intensity signal area on DWI and apparent diffusion coefficient(ADC) were measured in different groups Results 1. In ischemic group rabbits,the hyper-intensity signal area on DWI with declined ADC appeared at ischemic 1h.The hype-intensity signal areas on DWI at different times were larger than that at ischemic 1h and unchanged at 24h.The mean ADC at different times declined at first and then gradually increased.2.In reperfusion group rabbits: compared with ischemic 1h,the hyperintensity signal BR>area on DWI reduced while ADC increased at reperfusion 2 and 5h, but the hyper-intensity signal area on DWI enlarged with ADC high at reperfusion 11h,then the hyper-intensity signal area on DWI enlarged with ADC reduced siginificantly at 23h and 47h.Conclusion The hyper-intensity signal area on DWI and the decreasing ADC in acute cerebral ischemia could be improved by early reperfusion,but the secondary decreasing ADC would be induced with