In situ composite fibers based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystalline polymer (Vectra A950) were prepared using a single-screw extruder. The fibers were taken up at selected speeds. The spinnability, thermal behavior, mechanical properties, and morphologies of the PEN/Vectra A950 blend were investigated. The results showed that the PEN/Vectra A950 blends were partly miscible, and the miscibility increased with the increased concentration of Vectra in the blend. The DSC measurements indicated that Vectra enhanced the crystallization process of PEN by performing as a nucleating agent. The Instron tensile property study, coupled with scanning electron microscopy, revealed that the mechanical properties of the PEN matrix were significantly improved when Vectra existed as long and continuous fibrils. The laser Raman results showed that the Vectra orientation began to develop at take-up speeds above 500 m/min.