Fibre/fibre interaction in composite materials is a very important micromechanical phenomenon that dictates the composite mechanical behaviour especially the toughness and failure process. A number of models have been developed to predict the fibre/fibre interaction in composite materials, but none of the existing models has considered the effect of interphase toughness on fibre/fibre interaction. In this study, micro-Raman spectroscopy (MRS), with the ability to measure strain in graphite fibres with a spatial resolution of 2 µm, was used to measure fibre/fibre interaction in graphite/epoxy model composites with three different interphases. An energy-based model was used to calculate the strain energy release rate (Gi) for the three interphases used in this study. The three interphases, unsized, sized, and PMMA coated, yielded strain energy release rates of 40, 30, and 10 J m−2 respectively. Using the values calculated for strain energy release rate of the interphase and interfacial crack length, the energy-based model predicated stress concentration factor values in agreement with those experimentally measured.