The Lewis and Brønsted acidic properties of the surface sites of a high surface area tin(IV) oxide sample were investigated by the CO adsorption at low temperature using IR spectroscopy. Two distinct cus (coordinatively unsaturated sites) Sn4+ cation sites having different Lewis acidic strength have been evidenced: (i) Sn4+I strongly bonding CO (νCO = 2210-2196 cm−1), (ii) Sn4+II (νCO = 2183-2177 cm−1), being less acidic. Several types of OH groups have been also evidenced: (i) OH occluded in the bulk and inaccessible to CO (νOH = 3445-3435 cm−1), (ii) non-acidic OH groups (νOH = 3740-3725 and 3660 cm−1) which give rise to a νCO band at 2155 cm−1 and νOH bands respectively at 3640 and 3570 cm−1 (ΔνOH = 90 cm−1) as CO adsorption occurs, (iii) slightly Brønsted acidic OH groups (νOH = 3625 cm−1) which lead to a νCO band at 2164 cm−1 and a νOH band at 3740 cm−1 (ΔνOH = 155 cm−1). Depending on the treatment in vacuum (at room temperature or at 773 K) prior to CO adsorption, the populations of these different sites may vary. An outgassing in vacuum at 773 K leads to the partial dehydroxylation of the SnO2 surface, increasing the number of Sn4+ Lewis acidic sites.