La_1-xSr_xMnO₃ nanoparticles were synthesized by precipitation from diethylene glycol solution. Features of synthesis were studied using ¹Н, ¹³С, ¹³⁹La nuclear magnetic resonance (NMR) investigations. The obtained results showed that the complexation reaction between diethylene glycol and metal cations takes place during the synthesis. These complexes decomposed at 200 ℃ and an amorphous precursor (La,Sr)MnO₃ was formed. According to X-ray results, the crystallization of the perovskite structure began at 600 ℃ and finished at 800 ℃. Microstructural studies showed that obtained nanoparticles are weakly agglomerated and have small sizes. Based on these nanoparticles, magnetic fluid was prepared which was effectively heated under an alternating magnetic field.