The development of morphology during fiber spinning of blends of polyesters (PET and PET) with LCP (PET/HBA) was studied. The quantitative predictions of the blend morphologies under isothermal and non-isothermal conditions were obtained using a droplet deformation criteria based on the reduced capillary number and the affine deformation theory. The temperature, radius, velocity, and strain rate profiles of 60/40 polyester/LCP fibers along the spin line were calculated using Kase and Matsuo's theory for fiber spinning under the steady-state condition. Simulation of breakup of LCP phase during fiber spinning of the blend based on the dimensionless breakup time indicated the absence of their breakup. The flow curves of the blends at various temperatures required to carry out simulation were obtained by a capillary rheometer. An Arrhenius type equation was established for the viscosity variation with the temperature. An interfacial tension between the components was calculated from the interfacial thickness observed by SEM. In the calculation, various viscosity ratios between thermoplastics and LCP components were applied. Initial and final sizes of LCP phase were examined by SEM and image analyzer. The calculated diameters of LCP fibrils in the fibers were found to be in agreement with the measured values. (C) 2000 Elsevier Science Ltd. All rights reserved.