The synthesis and crystal structure of the bis (3-dimethylammonium-1-propyne) pentabromobismuthate(III) salt are given in the present paper. After an X-ray investigation, it has been shown that the title compound crystallizes at 298K in a centrosymmetric monoclinic system, in the space group C 2 /c with the following lattice parameters a=12.9034(3)Å, b=19.4505(6)Å, c=8.5188(2)Å, β=102.449(2). Not only were the impedance spectroscopy measurements of (C 5 H 10 N) 2 BiBr 5 carried out from 209Hz to 5MHz over the temperature range of 318K–373K, but also its ac conductivity evaluated. Besides, the dielectric relaxation was examined using the modulus formalism. Actually, the near values of activation energies obtained from the impedance and modulus spectra confirms that the transport is of an ion hopping mechanism, dominated by the motion of the H + ions in the structure of the investigated material.