A series of rare-earth compound RE2 L2 (HL) 2 (H2O) 6 · 2H2O (RE= La, Nd, Eu, Tb, Er, Y) containing 3-nitrophthalic acid(H2L) ligand were synthesized from ethanol-water solution, and characterized and investigated by the element analysis, infrared and ultraviolet absorption spectra and different thermal-thermogravimetric analysis. The results of the spectroscopic analysis were conformed to the crystal structures determined by X-ray diffraction, showing that the carboxylate (-COO-) and carboxyl (-COOH) groups of the ligand link to the rare-earth ions by bridging and terminal mode respectively. Two rare-earth ions were linked by two di-deprotonated ligand L^2- in bridging-chelating mode to form a dinuclear structure, and coordinated by the other two mono-deprotonated ligands HL-in terminal chelating mode using their carboxylate (-COO) and carboxyl (- COOH) group together, respectively. The IR spectra shows the existence of the carboxylate (-COO-) and carboxyl (- COOH) group and the hydrogen bond interactions between the carboxyl (-COOH) group and crystal water. The DTA-TGA data were consistent with the composition of compounds, exhibiting an endothermic peak of the loss of the crystal and coordinated waters at about 150℃ and two exothermic peaks of the oxidation and decomposition of ligands in the rang of about 340 to 460℃.