We investigated the use of the T2 mapping technique to quantitatively evaluate the thigh muscles of 18 dermatomyositis (DM)/polymyositis (PM) patients and 10 healthy control subjects. Moreover, the correlation of T2 values with apparent diffusion coefficient (ADC) values was also studied. The results showed significantly elevated T2 values with edematous muscles and increased T2 values with unaffected muscles (normal appearing in conventional MRI) in DM/PM patients, compared to the control group. The T2 values of the edematous muscles were found to be closely correlated with the ADC. This study demonstrated that T2 mapping may be successfully used in the quantitative evaluation of inflammatory myopathy.