Abstract The study of low-temperature X-ray diffraction and magnetic properties of VO 2 (B) has revealed a structural phase transition and formation of V 4+ ion pairs. The phase transition occurs over a temperature range from 300 to 180 K; however, a complete structural change is not attained. The low-temperature phase has the same monoclinic symmetry as the high-temperature phase. The X-ray Rietveld refinements revealed a significant decrease in the V(2)-V(2) distance from 0.2867 to 0.2670 nm, indicating V 4+ - V 4+ pairing for half of the V sites in the low-temperature phase. The pairing has been confirmed by the observation of a spin-singlet state in the 51 V NMR measurements and corresponds to the decrease in magnetic susceptibility. The behavior of phase transition and pairing in VO 2 (B) are analogous to those in V 6 O 13 , which has a related structure.