Various titanium(IV) complexes of the type Cp＇Ti(OAr)Cl-2 (Cp＇ = cyclopentadienyl; OAr = aryloxy) could be prepared in high yields from Cp＇TiCl3. Cp*Ti(O-2,6-(Pr2C6H3)-Pr-i)Me-2 (Cp* = C5Me5) could also be prepared from Cp*TiMe3 with 2,6-(Pr2C6H3OH)-Pr-i in high yield(77%). These complexes showed notable catalytic activities for ethylene polymerization with MAO or (AlBu3)-Bu-i-Ph3CB(C6F5)(4) : Cp*Ti(O-2,6-(Pr2C6H3)-Pr-i)X-2 [X= Cl (2b), Me (8b), CF3SO3 (9b)] showed the highest activities among these complexes. The effects of substituents on both cyclopentadienyl (pentamethylcyclopentadienyl) and aryloxy (2,6-diisopropylphenoxy) groups are important for the remarkable activity. The crystallographic analyses of CpTi(O-2,6-(Pr2C6H3)-Pr-i)Cl-2 (Ib), Cp*Ti(O-2,6-(Pr2C6H3)-Pr-i)Cl-2 (2b), and (1,3-(Bu2C5H3)-Bu-t)Ti(O-2,6-(Pr2C6H3)-Pr-i)Cl-2 (6b) could be performed, and the bond angle of Ti-O-C (phenyl group) for 2b (173.0 degrees) was found to be significantly different from those for other complexes (162.3-163.1 degrees), although no significant differences are observed for other bond lengths and angles among these compounds. CpTi(O-2,4,6-Me3C6H2)(2)Cl (7a) and CpTi(O-2,6-(Pr2C6H3)-Pr-i)(2)Cl (7b) could be prepared from CpTiCl3 with the corresponding phenol under the refluxing conditions of toluene, and the structure of 7a could be determined by X-ray crystallography. These complexes also exhibited moderate catalytic activities for ethylene polymerization in the presence of MAO, which was prepared by removing toluene and an excess amount of AlMe3, and the effect of the bulk of phenoxy ligand on the activity was demonstrated. 2b was also found to be an effective catalyst precursor for ethylene/1-butene copolymerization, and the smaller r(E)r(B) values (0.25-0.36) compared to [Me2Si(C5Me4)((NBu)-Bu-t)]TiCl2 (2.45) were observed by microanalysis of the resultant copolymers.