The title complex [Sm(o-MBA)(3)phen](2) (o-MBA, o-methylbenzoate; phen, 1,10-phenanthroline) was prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra and TG-DTG techniques. The results show that the crystal is triclinic, space group P (1) over bar with a = 13.1364(10) angstrom, b = 14.3739(11) angstrom, c = 17.4356(13) angstrom; alpha = 83.1100(10)degrees, beta = 83.7760(10)degrees, gamma = 73.0520(10)degrees, Z= 2, D-c = 1.568 Mg/m(3), F (000) = 1476. The crystal is consisted of two similar types of binuclear molecule. Each Sm3+, is nine-coordinated by one bidentate chelating carboxylate group, two bidentate bridging and two tridentate chelating-bridging carboxylate groups, as well as one 1, 10-phenanthroline molecule. The thermal decomposition mechanism of [Sm(o-MBA)3phen]2 has been determined on the basis of thermal analysis. The dependences of E -alpha for the first-stage decomposition process were determined by using Ozawa-iterative procedure, which show the E values varied with the extent of conversion. In addition, the lifetime equation at weight-loss of 10% was deduced as ln tau = -25.5547 + 18511.68/T by isothermal thermogravimetric analysis. (C) 2005 Elsevier B.V. All rights reserved.