[en] The electronic structure of impurity atoms of 3d-transition metals substituting the Cu node in the copper-oxygen chain of YBa₂Cu₃O₇ compound is determined. It is shown for Cr, V, Ti and Sc impurity atoms that the closer is the impurity atom to the beginning of the 3d-series, the higher is the energy of the d-band centre and the weaker is hybridization of d-states of the impurity with p-states of oxygen atoms of the chain. In case Co, Fe, Mn magnetic impurities strong hybridization of d-states of the impurity and p-states of surrounding oxygen atoms is observed. Co, Fe, Mn impurity atoms have local magnetic momenta and the Fe atom momentum is greater than those of Co and Mn atoms