Synergistic effect of the mixed phase in titania photocatalyst on its performance compared to the pristine phases has been investigated in terms of the bulk and interfacial behavior of the phases in contact. The experiments were conducted under both UV and visible light irradiations. The photoactivity variation has been correlated with the changes in the ratio of anatase to rutile phases (A/R ratio), and their unique response to UV and visible radiations. For this, a set of pure (rutile or anatase) and mixed phases (with varying AIR ratio) titania nanoparticles were synthesized. The physicochemical characterization was done using SEM, XRD, EDAX, UV-DRS, PL and FTIR analyses. The activity of catalysts in UV and visible light was investigated by monitoring the degradation of phenol. The results show that the mixed phase catalysts show enhanced photoactivity compared to pristine phases across the irradiation wavelength range. Further, the catalysts having a narrow range of high AIR ratio (> 1) around 5.0 show high UV activity while those having low A/R ratio (< 1) around 0.5 show high visible light activity. A mechanism is proposed based on the influence of interfacial phenomena under both UV and visible light irradiations. It explains the differences observed in the behavior of the catalyst irradiated with UV and visible light and also the high activity of mixed phase catalysts compared to the pristine phases across the wavelength ranges. (C) 2011 Elsevier B.V. All rights reserved.