Visible-infrared sum frequency generation (SFG) has been applied to probe molecular species on the surface of nanoparticulate anatase TiO2 films. A trace hydrocarbon film on the surface, not detected by Fourier transform infrared spectroscopy (FTIR), is easily sensed with SFG. The first direct observation of hydroxyl groups (-OH) on the TiO2 film surface by SFG is reported. A broad vibrational band with multiple peaks in the region of 3500-3800 cm(-1) ascribed to OH groups reflects the surface heterogeneity of the material.