Rare-earth nano-materials with controlled structures are of great interest owing to possible luminescent and magnetic properties resulted from lanthanide cations, and thus promise many applications, such as in solar cells and biological labeling and imaging. Host matrices used in these materials usually were Ln ions, but it was problematic to prepare low-valent lanthanide materials on nano-meter scales. Low-valent lanthanide mono-chalcogenide nanocrystals (NCs), and especially stable europium mono-chalcogenide EuX (X=O, S, Se, and Te) NCs started to become available with appealing optical and magnetic properties. The EuX NCs have degenerate 4f orbitals which locate between the conduction band (5d orbitals of Eu) and the valence band (p orbitals of O , S , Se , and Te ). Their 4f–5d electronic transitions and spin configuration lead to unique magneto-optical properties. During the past a few years, several research groups reported various routes to prepare the EuXNCs, such as with high temperature reduction, thermal or optical decomposition of single-source precursors, and a liquid-phase synthesis. However these methods usually required special instruments and extra ligands for Eu, which were time-consuming with the product; meanwhile, the resulting EuX NCs exhibited poor optical and magnetic properties, with little potential in applications. Moreover, these previous studies focused on, mostly, the magnetic property of the EuX NCs, especially EuS NCs. The optical properties of the EuX NCs were rarely reported. Though it has been acknowledged that bulk EuX does not exhibit luminescence at room temperature, while surfacemodified EuO and EuS exhibited characteristic luminescence under UV excitation. No luminescent EuSe NCs have been documented. It has been an enduring challenge to prepare high-quality EuSe NCs with good luminescent and magnetic properties as well as with controlled morphologies. Herein, we report a one-step synthesis of blue luminescent, magnetic EuSe NCs. Also, we present our data on the experimental parameters affecting the change of the morphologies. We propose that the formation of the EuSe NCs requires the amine to act as a reducing agent. Our approach is simple and effective, using EuCl3 (H2O)6 and elemental selenium as Eu and Se sources, respectively. The overall synthetic procedure for EuSe NCs is depicted in Scheme 1. This method demonstrates several advantages,