In this work, the morphologies of PMMA/PP/PS blends of different concentrations were studied and compared to the predictions of spreading coefficient, minimum free energy, and dynamic interfacial energy phenomenological models. Different morphologies than the ones predicted by the phenomenological models were observed in the case of PMMA matrix: a mixture of core-shell morphology (core of PP and shell of PS), dispersed PS, and subinclusions within the core when the concentration of PP was increased were obtained. The quantitative analysis of the morphologies indicated that when PMMA was the matrix, PS acted as an emulsifier. The study of the evolution of morphology in the case of 10/80/10 PMMA/PP/PS blends showed that when PMMA is added to the binary blend of PP/PS, threads of PMMA are formed and break up into droplets with a size comparable to the ones of PS forming a double dispersion type morphology, and then PMMA penetrates the drops of PS, forming a core-shell morphology with only one drop of PMMA inside a matrix. Subsequently, the core droplet of PMMA deforms and breaks up into smaller droplets.