To develop a high-dielectric constant composite of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and multi-walled carbon-nanotubes (MWCNTs) with desirable homogeneity, MWCNTs were treated with a nitro-sulfuric acid by ultrasonication. The chemically modified MWCNTs (a-MWCNTs) were characterized by Fourier transform infrared spectroscopy and a back-titration procedure. Improvement of the dispersibility of a-MWCNTs in polymer matrix, in comparison with unmodified MWCNTs in P(VDF-TrFE), was confirmed by field emission scanning electron microscopy. Electric behavior of the composites with different volume fraction of dispersed carbon nanotubes can be described by percolation theory, as well as the Maxwell-Wagner-Sillars mechanism. The percolation threshold (f (c) ) of composites with a-MWCNTs (f (c) = 0.0308) is larger than that of composites with MWCNTs (f (c) = 0.0216) due to better dispersion of a-MWCNTs in matrix and the reduction of aspect ratio of a-MWCNTs occurred in the modification procedure. The composite with 2.98 vol% (close to the percolation threshold) of a-MWCNTs has a dielectric constant of 592 at 100 Hz and room temperature.