Infrared photodissociation (IRPD) spectra of carbon dioxide cluster ions,(CO2)n+　with n=3–8, are measured in the1000–3800 cm–1 region. IR bands assignable to solvent CO 2 molecules are observed at positions close to the vibrational frequencies of neutral CO 2 [1290 and 1400 cm–1 (ν1 and 2ν2),2350 cm–1 (ν3), and 3610 and 3713 cm–1 (ν1 + ν 3 and 2ν2 + ν3)]. The ion core in (CO2)n+ shows several IR bands in the 1200–1350, 2100–2200, and3250–3500 cm–1 regions. On the basis of previous IR studies in solid Ne and quantum chemical calculations, these bands are ascribed to the C2O+4 ion, which has a semicovalent bond between the CO2 components. The number of the bands and the bandwidth of the IRPD spectra drastically change with an increase in the cluster size up to n=6 , which is ascribed to the symmetry change of (CO2)n+ by the solvation of CO2 molecules and a full occupation of the first solvation shell at n=6.