Quaternary ammonium salts are well-known charge-control agents (CCAs) used widely in electrophotography. Aside from the CCA performance, a high thermal stability is also required because pulverized toners are prepared by kneading CCA with various toner components at 130-180 °C. Therefore, thermal stability has been studied in the present investigation in various quaternary ammonium salts with naphtholsulfonates in terms of structure analysis as well as IR spectra. As a result, the anions are found to play the key role in raising the melting point due to the formation of intermolecular OH^…O hydrogen bonds between the OH group of one anion and the sulfonic O atom of the neighboring one. The hydrogen bonds bridge anions either in the form of a onedimensional chain or a dimer.