Anew quaternary mixed anion complex of gadolinium (III), [Gd(CH3CH2COO)(2)(NO3) (phen)](2), was synthesized and structurally characterized. The ESR spectrum of the complex with effective g values of 5.314, 2.473 and 1.880 in polycrystalline powder at room temperature is quite different from the U spectrum. The coordination number of Gd 3, is nine with a monocapped square antiprism geometry. And the stacking effect was observed in the complex. The crystal of the complex belongs to triclinic with space group P (1) over bar, a = 0.9626(4) nm, b = 0.9732(4) nm, c = 1.1758(5) nm, alpha = 102.45(1)degrees, beta = 108.16(1)degrees, gamma = 96.68(2)degrees, V = 1.0018(7) nm(3), Z = 2, D-c = 1.80 g . cm(-3), mu(MoKalpha) = 33.63 mm(-1), F (000) = 530, GOF = 1.80, R = 0.023 and R-w = 0.027.