This paper deals with the preparation and characterization of nanocomposites of poly(ether ether ketone) (PEEK) containing nano-aluminum oxide (n-Al₂O₃) filler up to 30wt% (12vol%) loading. Nanocomposites showed improved thermal stability, crystallization, and coefficient of thermal expansion (CTE). Thermogravimetric analysis showed enhanced thermal stability and char yield on increasing the n-Al₂O₃ loading in PEEK matrix. The peak crystallization temperature is increased up to 13°C for the nanocomposites as compared to pure PEEK. The CTE is decreased to a value very close to the CTE of copper at 12vol% Al₂O₃ loading. The CTE values obtained were compared with the theoretical equations in the literature. The X-ray diffraction showed that PEEK crystalline structure is unchanged with addition of n-Al₂O₃. The distribution of n-Al₂O₃ in the PEEK matrix was studied by transmission electron microscopy and scanning electron microscopy. The results show that the prepared n-Al₂O₃/PEEK nanocomposites may have potential applications in electronics.