This document describes the flash method for the determination of thermal diffusivity of ceramic matrix composites with continuous fibre reinforcement. In order to conform with the unidimensional heat transfer hypothesis, the experimental conditions are defined such that the material behaves in a homogeneous manner. This involves performing tests in one symmetry axis of the composite. The method is applicable to materials which are physically and chemically stable during the measurement, and covers the range of temperature from 100 K to 2 800 K. It is suitable for the measurement of thermal diffusivity values in the range 10"4 m2"s"1 to 10"7 m2"s"1.