The morphology, thermal, mechanical, and dielectric properties of high-performance poly(etheretherketone)/Si3N4 nanocomposites fabricated by hot pressing were investigated. It was found that the coefficient of thermal expansion (CTE) and dissipation factor decreased significantly with increasing Si3N4 content, whereas thermal stability was affected slightly. A nanocomposite with 30 wt% Si3N4 exhibited about 45% and 23% decrease in CTE, below and above T-g, respectively. The glass-transition temperature (T-g) was increased up to 20 degrees C. Microhardness was improved by 20% at 10 wt% Si3N4 content and thereafter it improved slightly. Modified rule of mixture with beta = 0.1 or Halpin-Tsai model with xi = 4 fits well the microhardness. The dielectric constant and loss factor of the nanocomposites are quite low, and thermal stability is much higher compared with commercial products. Various models were also used to correlate CTE and dielectric constant. POLYM. ENG. SCI., 51:509-517, 2011. (C) 2010 Society of Plastics Engineers