A radio tag-mounting member for use in a pneumatic tire having a sponge material fixed to the pneumatic tire at a rim-mounted side surface thereof or/and a rim at a tire-mounted side surface thereof; and a radio tag having a portion for detecting an internal state of the pneumatic tire or/and a portion for recording identifying information of the pneumatic tire. The radio tag is inserted into and fixedly accommodated in an accommodating portion formed in the sponge material as a concavity or as a slit-shaped notch; or the radio tag is fixed to a surface of the sponge material.