Abstract: In the present paper, the crystal and molacular structure of (η⁵-CH₃C₅H₄)₃Hf(OC₆H₃Cl₃-2,6)₃ have been determined by X-ray diffraction method. The crystallizes structure belongs to monoclinic system with space group C₂₅h-P₂1/c and cell parameters a = 17.010(2)Å, b = 8.577(1)Å, c= 16.313(3)Å,β=101.52(3)°. There are four molecules in each unit cell, Z = 4. Within each molecule there is a non-crystallographic twofold axis which lies on the (010) plane through the Hf atom parting the molecule into two similar halves.Two methylcyclopentadienyl group and two oxygen atoms around the hafnium atom form a pseudo-tetrahedron.The angle between the two methylcyclopentadienyls is 125.33°. The angle O-Hf-Ois 103.71°.The bond length Hf-Ois 2.004-2.022Å, it is shorter than Hf-O single bond. The results show clearly that Hf-O bond is characteristic of some partial double bond.