BACKGROUND: The corticospinal tract is an important tract for conducting motor function. The majority of studies focus on lesions of the corticospinal tract on appearance and function, whereas observation of normal corticospinal pathways can also improve understanding of lesion outcomes. OBJECTIVE: To observe the normal adult corticospinal tract using a diffusion tensor imaging technique to analyze fractional anisotropy (FA) in different levels of the brain. DESIGN, TIME AND SETTING: Neuroimaging observation was performed in the MRI Department, First Affiliated Hospital of Kunming Medical College in China, from October 2005 to October 2008. PARTICIPANTS: A total of 30 healthy adults were selected from the Department of MRI, First Affiliated Hospital of Kunming Medical College in China, from October 2005 to October 2008, and people with nervous system symptoms and signs were excluded. METHODS: Participants with normal conventional MRI results underwent diffusion tensor imaging examination in a 1.5 T GE MRI (slice thickness 4-5 mm, slice gap 0) for gradient data acquisition from 15 directions. The scanning involved the entire brain from the inferior medulla oblongata to the inferior cranial plate. Imaging post-processing was performed to obtain FA values; a paired t-test was applied for statistical analysis. MAIN OUTCOME MEASURES: FA values of the bilateral corticospinal tract in the medulla oblongata, pons, cerebral peduncle, basal ganglia, corona radiata, and centrum semiovale. RESULTS: FA values in the medulla oblongata and centrum semiovale were similar (P > 0.01). FA values of left corticospinal tract were significantly greater than the right side in the pons, cerebral peduncle, basal ganglia and corona radiata (P < 0.01). CONCLUSION: FA values vary by brain levels, including pons, cerebral peduncle, basal ganglia, and corona radiata. Moreover, FA values of the left corticospinal tract pathway were greater than the right side, which may relate to right handedness.