Gadolinium orthoferrite GdFeO₃ nanoparticles were synthesized by co-precipitation of gadolinium and iron(m) hydroxides in a free impinging-jets microreactor followed by thermal treatment of co-precipitation products. According to X-ray diffraction, the co-precipitated hydroxides were X-ray amorphous, and the content of key elements within their composition corresponded to the stoichiometry of GdFeO₃. Powder X-ray diffraction of the product of thermal treatment of hydroxides at 750 °C for 4 h indicated on the formation of GdFeO₃ nanocrystals with a perovskite-like orthorhombic structure and an average crystallite size of 27±3 nm. Scanning electron microscopy showed that the gadolinium orthoferrite nanocrystals had an isometric morphology, and their specific surface area was determined by the Brunauer—Emmett—Teller method to be 13.55 m²g⁻¹. Mössbauer spectroscopy and vibrational magnetometry showed that the obtained GdFeO₃ nanoparticles were superparamagnetic and were characterized by a bimodal distribution of the effective field, indicating on their core—shell-type composite structure. The study of the composition, structure, morphology, and magnetic behavior of the obtained gadolinium orthoferrite nanoparticles showed that they can be used as a basis for contrast agents for magnetic resonance imaging (MRI).