Objective To investigate the role of quantitative analysis of T2 relaxation time in the magnetic resonance imaging (MRI) diagnosis of breast cancer. Methods The study enrolled patients with clinical breast masses who were examined using MRI at eight different echo times. The differences in T2 relaxation time of benign and malignant breast lesions were analysed. Results A total of 67 patients (67 breast lesions: 46 malignant, 21 benign) were examined. The mean ± SD T2 relaxation time was significantly lower in the 46 malignant lesions compared with the 21 benign lesions (82.69 ± 15.37 ms versus 95.48 ± 26.51 ms, respectively). The area under the curve was 0.731. Using 79.52 ms as the cut-off between benign and malignant breast lesions, a sensitivity of 85.7% and a specificity of 58.7% were obtained. Conclusions There was a significant difference in T2 relaxation time between benign and malignant breast lesions. The specificity of using T2 relaxation time alone for the differentiation of benign from malignant lesions was not high, but it could constitute a new adjunct in the MRI diagnosis of breast cancer.