Objective:To investigate the role of diffusion weighted imaging (DWI) in evaluating prognoses of patients with hyperacute cerebral infarction after thrombolysis.Methods: A total of 112 patients with hyperacute cerebral infarction underwent MR examination (including routine MR and DWI) before thrombolysis.Forty-six patients met the standard of thrombolysis and were treated with rt-PA.Control group included 48 patients who did not meet the thrombolysis standard and were treated routinely.The other 3 patients had a poor MRI quality due to metal denture or other fillers.Fifteen patients had the onset of TIA and received conservative treatment.The measurements included the infarction volume,location,margin and ADC value of the progression area.Correlation analysis was conducted between the above parameters and the related parameters after thrombolysis to assess their roles in evaluating of patients prognoses.Results: There was no significant difference in the ADC values of different areas of DWI between the control group and thrombolysis group (P=0.07,0.46,0.71,and 0.34).Significant correlation was found between the infarction volume with the NIHSS score,length of hospital stay,mRS,and intracerebral hemorrhage(ICH)(P=0.009,0.034,0.048,and 0.015,respectivley).The larger the volume of infarction was,the higher the NIHSS score and the more the possibility of ICH.Conclusion: The determination of cerebral infarction area by DWI may help to evaluate the prognoses of patients with hyperacute cerebral infarction after thrombolysis; the ADC value only play a little role for the evaluation.