The thermal expansion behaviour of polymer composites having amatrix of polystyrene containing aluminium nitride (AlN) reinforcement hasbeen investigated under a special dispersion state of filler in the composite:AlN filler particles surrounding polystyrene matrix particles. It is found thatthe coefficient of thermal expansion (CTE) of the composite is about 0.3 ofthat of polystyrene at about 20% volume fraction of AlN. The particle size ofthe polymer matrix is also found to have an effect on the thermal expansion ofthe polymer composite under this dispersion state. The dependence of thetransition temperatures of the polystyrene on the AlN concentration andpolystyrene particle size has also been studied. The experimental CTEs ofcomposites have been compared with Kerner, Turner and Thomas models. TheThomas expression more closely matches the behaviour of polystyrene-AlNcomposites.