In this study the nanoparticles (NPs) of InN, TiO2 and their composites of varying sizes have been synthesized by hydrothermal and sol-gel methods and characterized with different analytical techniques including XRD, SEM, TEM and optical absorption spectroscopy. Two different composite NPs with smaller InN adsorbed on larger TiO2 NPs (InN:TiO2) and vice versa (TiO2:InN) have been fabricated and studied for their opto-electronic and photo-catalytic properties. The former was found to have a very broad UV-Vis absorption spectrum extending from 390 nm to much beyond 800 nm; however, no photo-catalytic activity was observed under the irradiation of a Xe-lamp and no photo- luminescence (PL) was detected upon excitation at 230 nm. On the other hand, the latter composite was found to have a similar but a smaller absorption between 390 nm and 500 nm, with an increasing absorptivity at longer wavelengths. In addition, the TiO2:InN composite was found to exhibit a broad PL peak between 325 and 410 nm together with two sharper ones at 425 nm and 480 nm upon excitation at 230 nm. The photo-catalytic activity of the TiO2:InN composite NPs was found to be similar to that of pure TiO2 NPs under Xe-lamp irradiation.