Selective adsorption is an important approach to separate organic molecules. In this study, an extraordinary selective adsorption capability of the rutile TiO2 (111) surface toward aldehyde over alcohol and carboxylic acid has been demonstrated on the basis of in situ photoelectrochemical (PEC) measurements. The adsorption strength of benzaldehyde on the rutile (111) surface has been investigated through the analysis of thermodynamic and kinetic properties of photodegradation processes using ex situ PEC measurements. The comparative results with rutile {111} and anatase {101} faceted electrodes demonstrate that there is a strong adsorption of benzaldehyde on the rutile (111) surface. The high ability of the rutile (111) surface for selective adsorption of aldehyde can therefore be utilized as a new approach to separate and purify aldehyde in industry.