The hydrogen-bonding supramolecule with 4-ethoxyanilinium and crown-6 is introduced to [Ni(dmit)2]- salt. The arrangement of supramolecular cations formed a three-dimensional structure with the one-dimensional channel filled with [Ni(dmit)2]- anions. The temperature-dependent structural analyses and DSC measurement disclose the first-order phase transition occurred around 285 K, where the lattice parameters show an abrupt change without a space group change. The title compound crystallizes in No. 1 space group P-1 and is piezoelectrically active with d33 value of 4.8 pC N-1. The frequency- and temperature-dependent dielectric constants and potential energy calculation are consistent with the forward-backward motion of the ethoxyl group in the cation.