The present study is directed to clarify the influence of the ratio of anatase to rutile phase, containing in the TiO2 samples, on their activity as photocatalysts in slurry. A series of samples corresponding to different percentages of anatase is prepared from commercial anatase and rutile TiO2 brands (KRONOS). The crystalline phase composition of the samples is characterized by X-ray diffraction. The photocatalytic action of the mixtures is tested in photodegradation of the commercial organic dyes Malachite Green Hydrochloride and Orange II in aqueous solutions under UV irradiation. Comparative tests with Degussa P-25 are performed. The apparent rate constants of the process are determined from the kinetic curves using appropriate models. They generally increase with the anatase ratio, being always larger for Malachite Green than for Orange II. (C) 2007 Elsevier B.V. All rights reserved.