Percolative dielectric composites of sulfonated poly(aryl ether ketone) (SPAEK) and acidified graphite nanosheets (AGSs) were fabricated by a solution method. The dielectric constant of the as-prepared composite with 4.01 vol % AGSs was found to be 330 at 1000 Hz; this was a significant increase compared to that of pure SPAEK. Through the calculation, a low percolation threshold of the AGS/SPAEK composite was confirmed at 3.18 vol % (0.0318 volume fraction) AGSs; this was attributed to the large surface area and high conductivity of the AGSs. Additionally, our percolative dielectric composites also exhibited good mechanical performances and good thermostability, with a tensile strength of 71.7 MPa, a tensile modulus of 1.91 GPa, a breaking elongation of 16.4%, and a mass loss temperature at 5% of 336°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40028.