Abstract: The effect of oxygen in the suspension polymerization of tetrafluoroethylene initia-ted by ammonium persulfate has been investigated．As usual，oxygen acts as an inhibi-tor in this radical initiated polymerization and the induction period increases with the amount of oxygen present in the system．In the presence of oxygen，pH of the aqueous medium drops considerably after polymerization，with simultaneous production of fluoride ions, the concentration of which increases with botll the amount of oxygen and poly-merization conversion．The product obtained from the polymerization of tetrafluoroethylene in the presence of oxygen contains considerable amount of carboxylic and carboxylate groups as in-dicated by its infrared spectra．According to the measurements of fluoride ion and oxalic acid concentrations of the resulting aqueous medium，it seems that the polymeric peroxide，七(CF2一CF2)n一O—O+，formed in the initial stage of polymerization in the presence of oxygen，does not decompose instantaneously and completely during the course of polymerization．The value of n is generally greater than one．The heat stability of the polymers thus formed is poor--low in thermal decomposi-tion temperature and fast in thermal decomposition rate．The initial thermogravimetric loss is probably due to the decomposition of carboxylate groups attached in the polymer．