Effect of annealing temperature on the stress and structural properties of a Ge core fibre via the molten core drawing (MCD) method is investigated using Raman spectroscopy, Scanning electronic microscopy (SEM), and X-ray diffraction. The experimental results showed that the Raman peak position of the Ge fibre shifted from 297.6 cm(-1) to 300.5 cm(-1), and the FWHM value decreased from 4.53 cm(-1) to 4.31 cm(-1), when the annealing is carried out at 700 degrees C, 800 degrees C, and 900 degrees C, respectively. For the Ge core annealed at 900 degrees C, an apparent crystal grain can be seen in the SEM image, and the diffraction peaks of the (331) plane are generated in the X-ray diffraction spectra. These results show that optimising the annealing temperature allows the release of the residual stress in the Ge core. When the Ge core fibre is annealed at 900 degrees C, it exhibits the lowest residual stress and the highest crystal quality, and the quality improvement relative to that of the sample annealed at 800 degrees C is significant. Hence, annealing at around 900 degrees C can greatly improve the quality of a Ge core fibre. Further performance improvement of the Ge core fibre by annealing techniques can be anticipated. (C) 2017 Elsevier B.V. All rights reserved.