Purpose: Breast 3.0 T Magnetic resonance diffusion-weighted images (MR-DWI) of benign and malignant lesions were obtained to measure and calculate the signal-to-noise ratio (SNR) and signal intensity ratio (SIR) of lesions at different b-values. The variation patterns of SNR and SIR were analyzed with different b- values and the images of DWI were compared at four different b-values with higher image quality. The effect of SIR on the differential diagnostic efficiency of benign and malignant lesions was compared using receiver operating characteristic (ROC) curves in order to provide a reference for selecting the optimal b-value. Materials and Methods: A total of 96 qualified patients with 112 lesions and 14 patients with their contralateral 14 normal breasts were included in this study. The single-shot echo planar imaging (EPI) sequence was used to perform the DWI and a total of 13 b-values were used: 0, 50, 100, 200, 400, 600, 800, l,000, 1,200, 1,500, 1,800, 2,000, and 2,500 s/mm2. On DWI images, the suitable ROI were selected. The SNRs of normal breasts (SNRnormal), SNR of benign and malignant lesions (SNRlesions), and the SIR of benign and malignant lesions were measured on DWI with different b-values and calculated. The variation patterns of SNR and SIR values on DWI for normal breasts, benign lesions, and malignant lesions with different b-values were analyzed by using Pearson correlation analysis. The SNR and SIR of benign and malignant lesions with the same b-values were compared using ttests. The diagnostic efficiency of SIR with different b-values for benign and malignant lesions were evaluated using ROC curves Results: The signal intensity and SNR values of normal breasts decreased with increasing b-values, with a negative correlation(r = -0.945,P<0.01). The mean SNR values of benign and malignant lesions were negatively correlated(r = -0.982 and -0.947, respectively and P < 0.01), gradually decreasing with increasing b-values. The mean SIR value of benign lesions gradually decreased with increasing b-values, a negative correlation (r = -0.991,P < 0.01). The mean SIR values of malignant lesions gradually increased with increasing b-values between 0 and 1,200 s/mm2, where the best contrast ratio was observed for bvalues ranging from 1,000-1,200 s/mm2. The mean SIR value of malignant lesions gradually decreased with increasing b-values ≧ 1,500 s/mm2. For b-values of 600, 800, l,000, and 1,200 s/mm2, the sensitivity and specificity of SIR in identifying benign and malignant lesions gradually increased with increasing b-values, peaking at 1,200 s/mm2. Conclusions: Breast DWI had higher image quality for b-values ranging from 600 to 1,200 s/mm2 and was best for b-values ranging from 1,000 to 1,200 s/mm2. The SIR had the highest diagnostic efficiency in differentiating benign and malignant lesions for a b-value of 1,200 s/mm2.