Intratumoural fibrosis is associated with poor prognosis in breast cancer patients. Non-invasive detection of such fibrosis may contribute to the provision of personalised treatment regimens. Multi-parametric MRI, using a clinical MRI scanner and incorporating endogenous contrast mechanisms, was performed on MNU-induced rat mammary carcinomas to identify parameters sensitive to the detection and quantification of fibrosis. Magnetisation transfer MRI derived parameters correlated with percentage picrosirius red staining, which detects collagen I/III, major components of fibrosis, in this heterogeneous tumour cohort. These results strongly support the inclusion of magnetisation transfer in clinical MR breast imaging protocols.