To provide a method for preventing the condensation of a gas containing an alkyl iodide when carrying out fumigation by using the alkyl iodide.

This method comprises adding a propellant to the gas containing the alkyl iodide, and feeding the resultant mixed gas to a storehouse for the fumigation while keeping the temperature of piping or heating the piping in the fumigation method of feeding the storehouse for the fumigation through the piping with the gas containing the alkyl iodide generated by heating a fumigant in a vaporizing chamber. By the method, the alkyl iodide can be readily used as the fumigant without condensation by using a conventional vaporizing device for the fumigation or a fumigation device by methyl bromide.