The interface and thermal expansion behaviour of magnesium matrix composite (Mg--2Al) unidirectionally reinforced with continuous high modulus and high thermal conductivity carbon fibres Thornel K1100 prepared by gas pressure infiltration technique was studied. The structure of the fibre-matrix interface was analysed using light microscopy, SEM, EDS, and TEM. Composite samples were subsequently thermally cycled at the heating/cooling rate of 3 • C min −1 in the temperature range of 30 to 350 • C in an argon atmosphere to reveal their thermal expansion behaviour. K e y w o r d s : metal matrix composites (MMCs), Mg/C interface, thermal expansion, CTE