OBJECTIVE To investigate the morphological features of nonpuerperal mastitis on magnetic resonance imaging (MRI). METHODS MRI results of 27 patients diagnosed with nonpuerperal mastitis were retrospectively analyzed according to the Breast Imaging Reporting and Data System (BI-RADS). RESULTS According to the enhanced MRI results, 22 cases presented as nonmass-like enhancements and five cases presented as masses. For the 22 nonmass-like enhancement lesions, one case showed as a homogeneous enhancement and 21 cases showed as heterogeneous enhancements. In the 21 heterogeneous enhancement cases, 13 contained lesions of rim-like enhancement. With regard to the number of lesions with rim-like enhancement, 11 presented as multiple and two as single. In the five mass lesions, three presented as rim enhancements. Indications of rim or rim-like enhancement accounted for 59% (16/27) of all cases. For the 16 cases that presented with signs of rim or rim-like enhancement, the central hypointensity area surrounded by enhanced rim or rim-like entity showed as hyperintensity in 14 cases and hypointensity or heterointensity in two cases on T2-weighted imaging. CONCLUSIONS On contrast-enhanced MRI, most nonpuerperal mastitis presented as nonmass-like lesion with heterogeneous signal intensity. The observation of signs of rim or rim-like enhancement on contrast-enhanced MRI with central hypointensity areas showing as hyperintensity on T2-weighted imaging is suggestive of the possibility of nonpuerperal mastitis.