Provided is a method for producing low molecular weight polytetrafluoroethylene less likely to generate C6-C14 perfluorocarboxylic acids and salts thereof. The method for producing low molecular weight polytetrafluoroethylene includes: (1) feeding into an airtight container: high molecular weight polytetrafluoroethylene: and a gas mixture containing an inert gas and oxygen and having an oxygen content relative to the total of the inert gas and oxygen of 1 to 10 vol %; and (2) irradiating the high molecular weight polytetrafluoroethylene to provide low molecular weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×102 to 7.0×105 Pa·s.