Tetrathiofulvalene compounds are important components of charge-transfer complexes, which may be applied in various fields of scientific research and practical applications. Some of these compounds cannot be characterized by mass spectrometry. Here, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for the characterization of tetrathiofulvalenes. The samples could be easily desorbed and ionized to form singly charged ions, and mass spectra with isotopic resolution readily obtained. The mass spectrometric results for 26 compounds have shown that MALDI-TOF is more effective and convenient than other mass spectrometry methods, and resolves the problem of mass spectrometric characterization of tetrathiofulvalene compounds. Copyright © 2001 John Wiley & Sons, Ltd.