Model blends comprising a cross-polymerized diacetylene-containing polyester (PE) and poly[ethylene-co-(vinyl acetate)] (EVA) were prepared and their mechanical properties evaluated. The dependence of the Young＇s modulus of the blends upon composition has been modeled by using a variety of theories for the deformation of multiphase polymers. Deformation of the cross-polymerized polyester phase in the blends was monitored by using Raman spectroscopy. The polyester phases within the blends produce well-defined Raman spectra in which the C=C stretching bands undergo significant stress-induced band shifts during deformation of the blends. The results show that the Raman technique allows direct measurement of the stress in the polyester phase in a blend, independent of the overall deformation of the blend. Simultaneous deformation and Raman spectroscopy studies, therefore, give a unique insight into the deformation micromechanics of polymer blends.