A detailed study of Ru substitution at the Mn site in La0.7A0.3Mn0.9Ru0.1O3 (A=Ca, Sr, Pb, Ba) polycrystalline samples shows an unusual magnetic pair between Ru+4/Ru+5 and Mn+4/Mn+3 redox couple. As a result, in the entire 10 at. % Ru-substituted compositions, the TC varies only by 10–30 K. The similarity of Mn4+/Ru4+:eg parentage facilitates a redox interaction between Mn and Ru ions, Ru+4/+5/Mn+3/+4. Ruthenium (IV) low spin state has a magnetic moment of 2.7–2.9μB, and with an extended 4d orbital, it enhances exchange coupling between Mn and Ru sites. © 2000 American Institute of Physics.