Half-sandwich zirconium complex 3 containing tridentate carborane [S,S,O] ligand 2 [(HOC6H2R2-4,6)(CH2)SC(B10H10) C(Ph)2P=S, R=tBu] was synthesized by the reaction of CpZrCl3(Cp=η5-C5H5) with sodium salt of ligand 2. Zirconium complex 3 was characterized by elemental and NMR analyses. DFT calculations were also performed on complex 3 to analyze the stereochemistry. The results from DFT calculations indicate that structure S1, in which no sulfur atom bonds to the zirconium atom, exists at the lowest energy level. In the presence of methylaluminoxane(MAO), complex 3 exhibited good catalytic activities for ethylene polymerization and long life-time up to 10 h. Moreover, the complex 3/MAO system displayed excellent catalytic activities toword ethylene copolymerization with 1-hexene or polar olefins. Half-sandwich zirconium complex 3 containing tridentate carborane [S, S, O] ligand 2 [(HOC6H2R2-4,6) (CH2) SC (B10H10) C (Ph) 2P = S, R = tBu] was synthesized by the reaction of CpZrCl3 (Cp = η5-C5H5) with sodium salt of ligand 2. Zirconium complex 3 was characterized by elemental and NMR analyzes. DFT calculations were also performed on complex 3 to analyze the stereochemistry. The results from DFT calculations indicate that structure S1, In the no sulfur atom bonds to the zirconium atom, exists at the lowest energy level. In the presence of methylaluminoxane (MAO), complex 3 exhibiting good catalytic activities for ethylene polymerization and long life-time up to 10 h. Moreover, the complex 3 / MAO system displayed excellent catalytic activities toword ethylene copolymerization with 1-hexene or polar olefins.