The polymerization of six spiro compounds such as 1-oxaspiro[2.5]octa-4,7-dien-6-one (OSODO), spiro[anthrone-10,2＇-oxirane] (SAO), and 5,7-dibromo-(Br-2-OSODO), 5,7-di-tert-butyl-(tBu(2)-OSODO), 5,7-difluoro-(F-2-OSODO), and 4,5,7,8-tetrachloro-1-oxaspiro[2.5]octa-4,7-dien-6-ones (Cl-4-OSODO) were examined. Spiro compounds which carry substituents at the 4 and 8 positions or bulky substituents at the 5 and 7 positions such as SAG, tBu(2)-OSODO, and Cl-4-OSODO were reluctant to undergo polymerization. Br-2-OSODO gave a polymeric material in very low yield. OSODO and F-2-OSODO polymerized to give poly(1,4-phenylene oxide) and poly(2,6-difluoro-1,4-phenylene oxide), respectively. The polymerizability of these spiro compounds was explained by the steric effect of the substituents.