PURPOSE: To evaluate the effect of changes of parameters of diffusion tensor imaging (DTI), including slice thickness/slice number, b-value and the direction number of a diffusion gradient on fractional anisotropy (FA). MATERIALS AND METHODS: Three groups of normal volunteers underwent brain diffusion tensor imaging with the use of three different imaging parameters as follows: a different slice thickness/slice number (6 mm/20 slices and 2.33 mm/54 slices), a different b-value (800 s/mm2/1000 s/mm2) and a different number of directions of the diffusion gradient (6 and 15 directions). The signal to noise ratio (SNR) and FA were measured by a ROI measurement at the anterior corona radiata, superior corona radiata, putamen and corpus callosum. We compared the mean SNR and FA in each group by the use of the paired T-test. RESULTS: The SNR decreased and the FA increased significantly according to the increase of the slice number (6 mm/20 slices vs. 2.33 mm/54 slices). The SNR of DTI with 15 diffusion gradient directions was significantly higher than DTI with six directions, without a difference of FA. There were no significant changes of the SNR and FA of DTI according to the b-value. CONCLUSION: It is essential and useful in the clinical application of DTI to understand the effect of imaging parameters on FA.