Using the catalyst system composed of Cp2TiCl2 and i-C3H7MgCl, isoprene can be oligomerized to a mixture of dimers and higher oligomers. The two dimers 2,6-dimethyl-1, trans-3,6-octatriene and 3,6-dimethyl-1,3,6-octatriene were characterised by GC-MS; H-1-NMR; C-13-NMR and GC-IR. The effects of reaction time, molar ratio of catalyst to isoprene, temperature and solvent on the reaction were discussed. After established the appropriate reaction condition, the substituent effect of a series of alkyl ring-substituted cyclopentadienyl titanium dichlorides on catalystic activity were investigated. A mechanism of the reaction was also proposed.