Four manganite samples of the series, (La1/3Sm 2/3)2/3SrxBa0.33-xMnO3, with x=0.0, 0.1, 0.2 and 0.33, were investigated by X-band (∼9.5 GHz) electron paramagnetic resonance (EPR) in the temperature range 4300 K. The temperature dependences of EPR lines and linewidths of the samples with x=0.0, 0.1 and 0.2, containing Ba2 ions, exhibit similar behavior, all characterized by the transition temperatures (TC) to ferromagnetic states in the 110150 K range. However, the sample with x=0.33 (containing no Ba2 ions) is characterized by a much higher TC=205 K. This is due to significant structural changes effected by the substitution of Ba2 ions by Sr2 ions. There is an evidence of exchange narrowing of EPR lines near Tmin, where the linewidth exhibits the minimum. Further, a correlation between the temperature dependence of the EPR linewidth and conductivity is observed in all samples, ascribed to the influence of small-polaron hopping conductivity in the paramagnetic state. The peak-to-peak EPR linewidth was fitted to ΔBpp(T)=ΔB pp,minA/Texp(-Ea/kBT), with Ea=0.09 eV for x=0.0, 0.1 and 0.2 and Ea=0.25 eV for x=0.33. From the published resistivity data, fitted here to σ(T)∝1/T exp(-E σ/kBT), the value of Eσ, the activation energy, was found to be Eσ=0.18 eV for samples with x=0.0, 0.1 and 0.2 and Eσ=0.25 eV for the sample with x=0.33. The differences in the values of Ea and Eσ in the samples with x= 0.0, 0.1and 0.2 and x=0.33 has been ascribed to the differences in the flip-flop and spin-hopping rates. The presence of Griffiths phase for the samples with x=0.1 and 0.2 is indicated; it is characterized by coexistence of ferromagnetic nanostructures (ferrons) and paramagnetic phase, attributed to electronic phase separation. © 2010 Elsevier B.V.