The electronic structure and thermochemical stability of the HOX-SO3 (X = F, Cl, Br) complexes is studied using second-order Moller-Plesset perturbation theory (MP2). The calculated dissociation energies of the HOF-SO3, HOCI-SO3, and HOBr-SO3 complexes are 5.43, 6.02, and 5.98 kcal mol(-1) at MP2/6-311 ++G(3df,3pd) level, respectively. Anharmonic CH stretching frequencies of the HOX (X = F, Cl, Br) moieties along with the frequency shifts upon complex formation are calculated at the MP2/6-311 ++G(2df,2p) level. AIM and NBO analyses were also performed. Theoretical data strongly encourage performing of matrix-isolation studies of the title complexes and their spectroscopic identification.