The enhanced magneto-optical properties of nanoscaled lanthanide chalogenide semiconductors which have a wide energy gap were observed at around 500 nm for the first time. The nanoscaled semiconductors, Eu1-xSe nanoparticles 1 (cubic shapes) and 2 (spherical shapes), were synthesized by the thermal reduction of Eu(III) ion with organic ligands containing Se atoms. The resulting Eu1-xSe nanoparticles were characterized by X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, superconducting quantum interference devices magnetometer, and microwave induced plasma atomic emission spectroscopy measurements. The particle grain sizes of 1 and 2 were estimated to be 11 and 20 nm, respectively. The concentration-normalized Veldet constants (the magnitude of the Faraday effect) of Eu1-xSe nanoparticles were much larger than those of corresponding bulk EuSe and EuS nanoparticles.