We have grown a series of [PbMg1/3Nb2/3O3]((1-x)Lambda)/[PbTiO3](xLambda)(PMN1-x/PTx) superlattices for which the composition varies, 0.1less than or equal toxless than or equal to0.8, but the modulation period Lambda is kept constant at about 130 A. X-ray diffraction indicates that the polar c axis of the PT layers lies in the plane of the films. The Raman spectra, which reflect the sum of the spectra of PMN and the PT layers, confirm the a-domain orientation of the PT layers. A downshift of the E(1TO) soft mode of the PT layers was attributed to tensile stress, estimated to be in the range of 2.5-3.6 GPa, induced by the lattice mismatch of PMN/PT layers. We observe the splitting of the "silent" mode in PT into distinct modes B-1 and E and attribute this to the strains present in the layers.