The polyarylate TLCP (Thermotropic Liquid Crystal Polymer) fibers are used as super fiber like mooring ropes/cables and inflatable airbag for marine and aerospace industry because they are mechanically robust even in ocean and cryogenic temperature. To obtain high performance TLCP fibers, heat treatment is one of the important post-process to enhance mechanical properties of the as-spun fibers by solid-state polymerization increasing molecular weight. In this research, we demonstrated the different molecular weight TLCP fibers having high tensile strength, toughness, and thermal stability by optimized heat treatment condition. TLCP resins were consisted of polymerized p‐hydroxybenzoic acid (HBA) and 2‐hydroxy‐6‐naphthoic acid (HNA) with molecular ratio of 73:27. Two kinds of resin having different molecular weight supplied from Seyang Polymer Inc. in Korea were used and the TLCP as-spun fibers were produced by pilot-scale melt-spinning apparatus. Highly concentrated (>99.99 %) nitrogen gas was purged into oven and temperature was precisely adjusted from 240 ℃ to 300 ℃ in heat treatment process. Thermal properties and structural analysis of the TLCP fibers were conducted by differential scanning calorimetry (DSC), scanning electron microscope (SEM), and two dimensional wide angle X-ray diffraction (2D-WAXD). These results are discussed about structural change and mechanical properties of polyarylate TLCP fibers having different molecular weight by optimized condition of heat treatment such as temperature and time.