X-band electron magnetic resonance method was explored for study of sonochemically prepared nano-powders of La-based doped manganites: La0.7Sr0.3MnO3 and La0.9Ca0.1MnO3 at 115 <= T <= 600 K temperature interval, including main characteristic points of its magnetic transitions. The data obtained were compared with those for crushed bulk single crystals of the same compositions. It is shown that nano-powder of La0.7Sr0.3MnO3 has the same ferromagnetic ordering as its bulk counterpart, being more homogeneous and less anisotropic. While, nano-powder of La0.9Ca0.1MnO3 shows two distinct ferromagnetic phases in a marked contrast to the bulk sample, where complex magnetic structure comprising canted antiferromagnetic matrix and ferromagnetic clusters is observed. To explain the observed phenomena, the crucial role of nano-scale grain size and its interplay with spin and charge degrees of freedom in considered systems are discussed. (c) 2005 Elsevier B.V. All rights reserved.