SummaryOptical diffraction tomography (ODT) is used to reconstruct the complex refractive index distribution in cross‐sections of semi‐transparent, birefringent fibres. The selected fibres were polymer and animal fibres of either circular or non‐circular cross‐section with average thicknesses in the range 8–110 μm. This choice of samples was made to illustrate the imaging capabilities of ODT, and also to demonstrate some potential applications of the technique. The images representing the reconstructed refractive index distributions have a spatial resolution of about 2 μm, and show noticeable image contrast for refractive index variations of about 0·001. The ODT reconstructions compare well with refractive index information provided with the samples, and with scanning electron micrographs of cross‐sections of the same fibre samples. From these results it appears that ODT can be used to reconstruct the complex refractive index distribution in cross‐sections of semi‐transparent, b