Communication: MALDI-TOF MS characterizations of dihydroxy telechelic polyisobutylene is reported. Dichloro telechelic polyisobutylene (Cl-PIB-Cl) was synthesized by means of living cationic polymerization using p-dicumyl chloride/BCl3/DMSO initiating systems. The resulting polymer was functionalized by polymer analogous reactions to yield dihydroxy telechelic polyisobutylene (HO-PIB-OH). It was then investigated by MALDI-TOF MS in the cation mode using 1,8-dihidroxy-9(10H)-anthracenone (dithranol)/CF3COOAg matrix. The MALDI TOF MS spectra showed an increase in mass by 56 amu units attributed to the isobutylene monomer increment. The endgroups of HO-PIB-OH were determined. A good agreement was also found between the calculated isotope distributions and the isotope distributions determined by means of MALDI.