An RFID-tag coating rubber composition comprises: a rubber component; sulfur; silica; and a guanidine-based vulcanization accelerator, wherein the sulfur includes insoluble sulfur, and a content of the sulfur is 6.0 parts by mass or more with respect to 100 parts by mass of the rubber component. The RFID-tag coating rubber composition can achieve satisfactory communication performance, satisfactory resistance to cracking, satisfactory adhesiveness to an adjacent rubber member, and satisfactory elastic modulus simultaneously in a well-balanced manner and also is excellent in workability.