The title molecule,3-(4-(dimethylamino)benzylidene)-1,5-dioxaspiro[5.5]undecane-2,4-dione(I),was synthesized and characterized by elemental analysis,IR,UV-vis spectra and X-ray diffraction analysis.The compound belongs to the triclinic system,space group P1 with a=6.3640(6),b=7.7404(8),c=16.2890(18),α=86.860(2),β=85.837(2),γ=79.6720(10)o,V=786.60(14)3,Dc=1.331 g/cm3,and F(000)=336.Geometrical structure of the title compound was optimized by density functional theory(DFT)using B3LYP method with 6-31G**as the basis set.The vibrational frequencies were calculated by the DFT method and the results are consistent with the observed frequencies.The electronic absorption spectra were studied with the timedependent density functional theory(TD-DFT),showing the calculation results in good agreement with the corresponding experimental data. The title molecule, 3- (4- (dimethylamino) benzylidene) -1,5-dioxaspiro [5.5] undecane-2,4- dione (I), was synthesized and characterized by elemental analysis, IR, UV- vis spectra and X -ray diffraction analysis. The compound belongs to the triclinic system, space group P1 with a = 6.3640 (6), b = 7.7404 (8), c = 16.2890 (18),? = 86.860 (2),? = 85.837 ) = 79.6720 (10) o, V = 786.60 (14) 3, Dc = 1.331 g / cm3, and F (000) = 336. Geometrical structure of the title compound was optimized by density functional theory (DFT) using B3LYP method with 6-31G ** as the basis set the vibrational frequencies were calculated by the DFT method and the results are consistent with the implied scale frequencies. the electronic absorption spectra were studied with the time dependent density functional theory (TD-DFT), showing the calculation results in good agreement with the corresponding experimental data.