Abstract: The synthesis of metallacyclic derivative of niobocene dichloride, 1,2,3,4-tetraphenylbutadienebis (cyclopentadienyl) niobium (Ⅳ) are described. Solution and frozen-glass EPRspectra are measured. From computer simulation of the frozen-glass spectrum of Cp₃NbC₄ph₄, the values of the principal components of the g and Ttensors are g_x= 1.9915, g_y= 2.0017, g_z = 2.0005; T_x= -69.5G, T_y = - 103.2G, T_z=-18.0G. The observed anisotropy for the hyperfine interaction arises from the admixture of 4d_z² and 4d_x²-y² character in the HOMO, The ratio of mixing coefficients, a²/b₂=22.0.