The binary lanthanide catalyst for 1,3-butadiene was invented for 40 years ago. However, it has not been employed in cornmercial application due to its poor solubility and low activity. Nanosized neodymium chloride (NdCl3) was prepared in tetrahydrofuran (THF) medium through dissolution, chelation, and colloidal formation steps. Anhydrous NdCl3 was dissolved in THF, and ca. 1.5 THF molecules were coordinated. In the colloidal formation step, THF was slowly replaced with the addition of cyclohexane, and pale blue nuclei, nanosize below 200 nm, were formed. The structural studies for NdCl3 center dot xTHF using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) indicate that high ordered crystallinity is decreased with reduced particle size from trigonal prismatic to porous sphere structure. Nano NdCl3, obtained as colloidal state in cyclohexane, was activated with Al(iBu)(3) and Al(iBu)(2)H at room temperature and employed for 1,3-butadiene solution polymerization. The nanosized Nd catalysts showed high activity (1.0 - 1.3 X 10(5) g/Nd mol center dot h), which is comparable to that of the ternary neodymium catalyst Nd(neodecanoate)(3)/AlEt2Cl/Al(iBu)(3). The microstructures of polybutadiene, cis, trans, and vinyl, are about 96.0, 3.5, and 0.5%, respectively. (c) 2005 Wiley Periodicals, Inc.