Objective: Amyotrophic lateral sclerosis (ALS) is a multisystem condition which impairs white matter, corticospinal tract andfrontotemporal functions including cognition and behavior. This study aimed to perform diffusion tensor imaging (DTI) to de-tect white matter microstructural abnormalities, and also understanding the pathophysiology in ALS using 3T magnetic reso-nance imaging.Methods: The study examined 12 patients (7 males, 5 females) with sporadic ALS and 10 subjects in the control group (7 males,3 females) by voxel-based analysis of DTI with 3T MRI. We compared fractional anisotropy (FA) and apparent diffusion coefficient(ADC) parameters in the corticospinal tracts among patients who had ALS and those in the healthy control by DTI region ofinterest (ROI) and tractography techniques.Results: The FA and ADC measurements of the patient group were respectively 0.638±0.041 and 0.350±0.01 (p<0.001). Theresults of the healthy control group were respectively 0.701±0.054 and 0.288±0.027 (p<0.05). DTI showed decreased fractionalanisotropy in bilateral corticospinal tracts and internal capsule posterior crus. There was a correlation between the FA reductionsin this region and the severity of the disease in the patients with ALS.Conclusion: Consequently, with this longitudinal DTI study, the progress of upper motor fiber degeneration in ALS wasdemonstrated. It may be useful to utilize DTI to monitor the progress and effectiveness of treatment interventions, as well asunderstanding the pathophysiology of ALS.