The miscibility and phase behaviour of the ternary blend consisting of poly(epsilon-caprolactone) (PCL), poly(styrene-co-acrylonitrile) with 15wt% acrylonitrile (SAN15) and poly(styrene-co-maleic anhydride) with 14wt% maleic anhydride (SMA14) have been investigated by means of visual observations, light transmission measurements, differential scanning calorimetry (d.s.c.) and dynamic mechanical thermal analysis. The influence of the molecular weight of the components and of the blend composition is discussed. All crystallizable blends show two melting endotherms in the d.s.c. thermograms. The crystallization conditions were varied to examine this complex melting behaviour. The lamellar morphology of the semicrystalline blends was studied to obtain information about the most important morphological parameters (e.g. long spacing, thickness of the crystalline and amorphous layers, and width of the transition layer). On the basis of these morphological parameters, it was possible to get an idea about the type of segregation of the amorphous components (SAN15 and SMA14) in the blends during crystallization.