The rat brachial plexus has gained interest recently in neuro-regenerative research due to the advancement of neurosurgical equipment and techniques, but moreover in that it provides a model that can closely resemble the common peripheral nerve injuries seen in humans. The aim of this study was to provide a systematic baseline quantification for fibre type and morphology of the major terminal nerve branches of the rat brachial plexus (radial, ulnar and median) at four surgically accessible sites, through the forelimb. We applied a microstructural and immunohistological analysis of 12 rat brachial plexuses using three forms of micro-visualisation: electron microscopy; whole mount; and immunohistology. The three distal nerves studied showed a similar patterning in terms of the number and size of myelinated fibres, with all proportionally decreasing when moving distally. The fibre types of both the median and ulnar nerve appeared to be homogenously mixed throughout their trajectory, while the radial nerve had a more distinct patterning, especially distal to the elbow, with the entire nerve’s main branch appearing to consist of sensory fibres only. Our microstructural analysis of the rat brachial plexus provides important normative reference data for future peripheral nerve research using the forelimb of the rat.