The effect of thermoplastic addition on the cure kinetics and morphology of an epoxy/amine resin were investigated using differential scanning calorimetry (d.s.c.), dynamic mechanical spectroscopy and transmission electron spectroscopy. The results obtained from d.s.c. were applied to the Arrhenius, autocatalytic and diffusion controlled different kinetic models and showed that the effect of thermoplastic addition on the rate of cure was rather modest. The cure mechanism remained broadly autocatalytic in nature regardless of PSF concentration although at higher concentrations and lower cure temperatures, the mechanism became far more diffusion controlled. The residual miscibility of the epoxy/amine and thermoplastic phases within each other, however, caused the ultimate cure conversions and the conversions at gelation and vitrification to decrease with increasing PSF content while the Arrhenius activation energy increased with increasing cure conversion with increasing PSF content.