The crystallization behaviour of PBT and a reactive 50/50 PBT-PC blend were studied using synchrotron SAXS/DSC and TEM. The scattering data showed PBT crystallization to be inhibited in the blend due to PBT-PC transesterification, resulting in a progressive reduction in both melting and recrystallization temperatures and the degree of crystallinity developed. Analysis of the SAXS data using a one-dimensional correlation function showed PBT to exhibit an ordered lamellar morphology, whereas in the blend stacking of lamellae appeared to be inhibited. TEM of PBT-PC blends confirmed that PBT lamellae were randomly-oriented.