A series of novel ABA block copolymers containing a liquid crystalline polyester (A) block and an amorphous polyether sulfone (B) block were prepared. The block copolymers were characterized by FT-IR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, optical polarizing microscopy and X-ray diffraction measurement. Calculated results obtained from FT-IR spectra and a hydrolysis study reveal that the block copolymers contain 17-33% weight of polyether sulfone segments. All the prepared block copolymers have shown a liquid crystalline property. The block copolymer containing 33% polyether sulfone presented a glass transition at 180 °C and a crystalline to nematic phase transition at 278 °C. The other copolymers have exhibited only a crystalline to nematic phase transition at approximately 255 °C.