The polymerization of 5,7-dichloro-1-oxaspiro[2.5] octa-4,7-dien-6-one (Cl-2-OSODO) was carried out in 2-methoxyethanol using potassium 4-methoxyphenoxide as an initiator. The molecular weights of the polymers increased linearly with conversion. Monomer incremental addition and endcapping experiments exhibited the living characters of this polymerization. From kinetic studies of model reactions, a combination of fast initiation and slow propagation rates in this polymerization system was confirmed.