Abstract: Background and purpose: Intravoxel incoherent motion (IVIM) based on the theory of biexponential model is increasingly researched in the field of oncology. There is growing interest in the reproducibility of biexponential diffusion parameters. This study aimed to investigate the reproducibility of IVIM parameters of breast cancer based on different regions of interest (ROIs) and the influence of breast density, microcalcifications and histological grade on this reproducibility. Methods: In this retrospective study, 60 patients with breast cancer who treated in Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology underwent 3.0 T magnetic resonance imaging (MRI), including an IVIM diffusion-weighted imaging (DWI) examination with 12 different b-values (0-1 200 s/mm ² ). Two radiologists independently delineated different ROIs that were used to measure IVIM parameters ［true diffusion coefficient (D), pseudo-diffusion coefficient (D ^* ) and perfusion fraction (f)］. Intraclass correlation coefficients (ICC) were calculated to assess measurement reproducibility of the parameters. Variability between readers was assessed by using Bland-Altman 95% limits of agreement and analysis of variance (ANOVA). The effects of breast density, microcalcifications, and histological grade on measurement reproducibility were also assessed. Results: There was no significant difference in the IVIM parameters (D, f and D ^* ) among the three tumor ROIs. The intra- and interobserver reproducibility were good for D and f (ICC≥0.773). However, D^* had poor measurement reproducibility (ICC<0.75). Bland-Altman analysis revealed the narrowest 95% limits of agreement using the outlined-tumor ROI for D between readers. All breast cancer parameters were highly reproducible irrespective of breast density, histological grade or coexistence of microcalcifications (ICC≥0.811). Conclusion: Outlined-tumor ROI was more reproducible with respect to IVIM parameter measurements than the tumor fixed-radius ROI method. Breast density, microcalcifications and histological grade did not significantly affect the repeatability of the IVIM parameters.