This study investigates the dielectric properties of the aromatic thermoplastic polyimide ODFA–OOD in the region of α-relaxation. The films were obtained via a two-step synthesis followed by thermal treatment at 300 °C. Dielectric spectra were measured in the frequency range of 10⁻¹–10⁶ Hz and temperature interval of 473–573K. Analysis using the Havriliak–Negami function revealed the temperature dependence of relaxation parameters and the relationship between molecular mobility and the chemical structure of the polyimide.