A study of the magnetic, electrical resistivity and hyperfine properties of polycrystalline La 2RuO 5 compounds is presented in this work. This compound forms in a monoclinic phase (space group P2 1/c). Magnetic susceptibility measurements yield an effective magnetic moment which is consistent with spin S = 1 of Ru ions, and a negative paramagnetic Curie temperature which indicates the presence of antiferromagnetic interactions. Below T ∼ 165 K, the magnetization shows a sudden decrease, precisely where the electrical resistivity shows a change in the activation energy. Room-temperature perturbed angular correlation spectrum is well fitted considering two electric-quadrupole components. The temperature dependences of electric-quadrupole frequencies and asymmetry parameters corroborate the occurrence of a phase transition at T ∼ 170 K. Moreover, below 170 K, magnetic-dipole interactions, which coexist with electric-quadrupole interactions, are observed at Ru sites. This is considered as a strong evidence for the preservation of S = 1 moment of Ru ions in the triclinic phase. The temperature dependence of the magnetic hyperfine field shows an unusual behavior, not consistent with the Brillouin function, and suggests a first-order magnetic transition, associated with either a structural transition or an orbital ordering induced by the Ru-Ru pair formation. © 2012 American Institute of Physics.