Photoelectrochemical and photocatalytic properties of surface-modified rutile (001) surfaces of n-type titanium dioxide (n-TiO2) were investigated by photoassisted scanning probe microscopy. The n-TiO2 surface was modified by lapping and chemical etching which caused linear scratches and pyramidal etch pits on the surface, respectively. The photoelectrochemical efficiency of water oxidation was reduced by donorlike surface states produced on defect sites of the modified surfaces. Scanning photocurrent images of the chemically etched surface, taken with a conductive cantilever controlled by the atomic force feedback under UV illumination, revealed that these surface defects were localized at the bottom of irregularly etched steplike pits, whereas the regular faces of pyramid-shaped pits enhanced the photocurrents via the surface states formed in the band gap of n-TiO2. In situ atomic force microscopy indicated that photocatalytic deposition of platinum clusters in UV-illuminated solution preferably occurred on the scratches of the lapped n-TiO2 surface.