Mono-dispersed and smaller sized TiO2 nanospheres (-8 nm and -20 nm) exhibited superior photo-reductive efficiency for few aromatic aldehydes under UV light. It has been found that p-nitrobenzaldehyde and benzaldehyde are efficiently reduced to p-aminobenzyl alcohol (80% and 61%) and benzyl alcohol (59% and 38%) by 8 nm and 20 nm particles respectively, relative to negligible reduction by TiO2 (P25) under same experimental conditions. However, the successful photo-reduction of p-nitrotoluene (97%) was observed with P25 whose reduction potential (?0.5 eV) lies below the conduction band (CB, -0.85 eV vs NHE) of the catalyst. These findings can be explained on the basis of unsuitable and mismatched CB of P25 with respect to the lowest unoccupied molecular orbital of -CHO group to access its photo-activity. However, this hydrogenation occurred by synthesized smaller sized TiO2 particles (-8 nm and -20 nm) due to their favorable band gap (3.85 eV and 3.62 eV) and conduction band edge (-0.61 eV and -0.50 eV). Moreover, the other physio-chemical characteristics of 8 nm and 20 nm sized particles such as surface area (323 m2 g-1 and 297 m2 g-1), higher charge carrier relaxation time (61 μs and 40 μs) are also co-related for ease of photo-activity relative to TiO2 (P25).