Objective To study the diagnostic value of susceptibility weighted imaging (SWI) in diffuse axonal injury (DAI) and investigate the relationship between SWI and clinical prognosis. MethodsTwenty patients (15 males and 5 females) with DAI were included in this study. Routine sequences (T1WI, T2WI and FLAIR) and SWI were performed on a 3.0 T MRI scanner. There were 8 cases whose Glasgow score scale (GCS) ranged from 3.0 to 5.0, 4 cases from 6.0 to 8.0 and 8 from 9.0 to 12.0. The interval time between injury and examination were from 3 hours to 20 days. The number and volume of lesions observed on SWI and routine sequence were compared using Mann-Whitney U-test and paired t-test. Pearson correlation was used to analyze the relationship between the number and volume of all lesions and GCS. Results The lesions showed punctate, beaded, patchy and cord-like hypointense signal with various size on SWI (lesion diameter <2.0 cm). Distribution of lesions was multifocal with clear boundary. Routine MRI scan found a total of 78 lesions, while SWI sequence detected 424 lesions. The number of the lesions found on SWI was more than that on conventional MRI (U=-15.447,P＜0.01). The total volume of the lesions measured on routine MRI and SWI were 19 340 mm3 and 38 042 mm3, respectively. The total volume measured on SWI was more than that on routine MR (t=5.870,P＜0.01). The number and volume of all lesions were negatively correlated with GCS (r=-0.802, -0.767, P＜0.01). Conclusion SWI sequence could find more bleeding lesions than the routine MRI sequences. The number and the volume of the lesions were closely related to GCS. SWI showed high value in the diagnosis and prediction of the prognosis of DAI.