1-Octene was polymerized with TiCl4/MgCl2-AlEt3 and the polymerization was quenched with CH3COCl to introduce a CH3CO - group onto each propagation chain. The polymer was fractionated by fractional precipitation, and the number of active centers in each fraction was determined by measuring the CH3CO - content of the fraction. Distributions of the number and reactivity of active centers among the fractions were determined and discussed based on these experiments. The active center distributions were also studied by fitting the molecular-weight distribution (MWD) curve from GPC with multiple Schulz-Flory most-probable distributions. The uncontinuous reactivity distribution of active centers reveals that there exist limited types of active centers on the catalyst. Five types of active center were distinguished by the MWD fitting treatment. The correlations between the active center distributions and catalyst structures are discussed.