The relationship between the extensional flow properties and the morphology of fibers made from the thermoplastic blends (PS) containing a liquid crystalline polymer in spinning process, a typical extensional flow, has been investigated. The dispersed phase of the LCP exhibited microfibrillar structure which was more pronounced as the extrusion temperature increased. It turns out that the development of this structure could be explained using the information of the ratio of the extensional viscosities of both the dispersed and the matrix phases of the blends. This is because, as the extrusion temperature gets higher, the extensional strain rate in the spinline becomes larger resulting in a lower extensional viscosity ratio. Based on the fact that without spinning, no fibrillar structure was detected for all samples made with any extrusion temperatures, we also have found that the spinline extensional deformation, not the deformation within the capillary prior to the spinneret, is mainly responsible for the development of the microfibrillar structure of the LCP dispersed phase of the blends.