A cadmium complex constructed by the ligand 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) has been synthesized and its structure has been determined by means of X-ray single crystal diffraction. Crystal data for this complex are as follows: monoclinic, space group Cc, a=24.590(2), b=8.7882(7), c=13.8032(11) angstrom, =116.3350(10)degrees, V=2,673.3(4) angstrom 3, Z=4, F(000)=1,188. The central cadmium ion coordinates with two DMIT which constructed a distorted tetrahedron. Its third-order nonlinear optical property has been studied using Z-scan technique with 20ps pulses at wavelength 1,064nm. Its molecular second hyperpolarizability was determined to be 3.96x10-55 C center dot m4/V3.