A novel method of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of isobutylene homopolymers is reported in this paper. Because of the difficulty in attaching ions for such materials, the ionization for MALDI-TOF MS analysis is realized by sulfonating the olefin end groups to introduce a readily ionized moiety into the polymer. Polyisobutylene samples obtained from both living cationic polymerization and industral procedures are studied here, The number-average molecular weights and weight-average molecular weights of these materials were also measured by laser light scattering and vapor pressure osmometry. Results obtained from the three techniques agree closely with one another except for the fraction having the highest molecular weight. We postulate that this is due to the range of the molecular weight of this sample being too broad to be accurately measured by MALDI-TOF MS.