A new dinuclear terbium complex [Tb2(4-msal)6(H2O)4]·6H2O (1) (4-msal = 4-methylsalcylate) was synthesized. Its structure was determined by single crystal X-ray diffraction, and the complex was characterized by PXRD, FT-IR, fluorescence, TGA and DTA. Complex 1 exists as discrete molecules that are linked by extensive O–H … O hydrogen bonds into a 3D network. The luminescence lifetimes of 3 μm methanol solution and solid sample of 1 are 1.321 and 1.009 ms, respectively. The quantum yield of solid sample is 6.0%. The luminescence quenched more than 50% when 3% (vol/vol) different impurities (acetone, acetonitrile, chloroform, dichloromethane, dioxane, DMF, DMSO, ethanol, ether, ethyl acetate, glycol, H2O, hexane, TEA, THF and toluene or their mixture) were added. The inverse linear relationship between the Lg value of fluorescence intensity and the volume ratio of the minor component (to a maximum of 20%) is interpreted in terms of LgI = a−bX (I: luminescence intensity; X: volume ratio of impurities in methanol; a, b are constants). So 1 is a potential luminescent sensor for analyzing the purity of methanol.