The tensile strength distribution of fibres is a key constitutive property of fibre reinforced composites and is often described using Weibull statistics. However, the standard experimental methods used for obtaining the Weibull parameters are tedious and prone to error. In this paper, Weibull parameters of polycrystalline α–Al2O3 fibres (Nextel 610) are determined from piezospectroscopic measurements using photostimulated Cr3+ luminescence (fluorescence) during fibre bundle tests. The fibre bundle stress, the stress on the surviving fibres and the survival probability can all be obtained by deconvolution of the luminescence spectra. Furthermore, a qualitative method is developed to assess whether the fibres in a bundle are aligned by monitoring the broadening of luminescence linewidth as a function of the applied load. The tensile strength distributions of Nextel 610 fibres are evaluated in the as-received condition and following heat treatments at 1000, 1200 and 1300 degrees C in air. The strength of fibres extracted from an Al–0.8 per cent Mg alloy matrix composite are also characterized. The results show a significant strength degradation after heat treatment above 1000 degrees C with a broadening of the fibre strength distribution. The test of the extracted fibres also indicates no degradation in fibre strength during processing of a metal matrix composite (MMC) at 780 degrees C.