Degradation of hexazinone has been investigated by means of photocatalysis of mixed-phase crystal nano-TiO2. Influences of adsorption, amount of nano-TiO2, pH and irradiation time on the photocatalytic process are studied. Results show that hexazinone is totally degraded within 40 min of irradiation under pH neutral conditions. This compares favorably with Degussa P25 TiO2 when conducted under the same experimental conditions. Preliminary photocatalytic kinetic information for hexazinone degradation is proposed. First order kinetics is obtained for the adsorption and photocatalytic degradation reactions, which fit the Langmuir-Hinshelwood model. A rapid, sensitive and accurate UPLC-MS/MS technique is developed and utilized to determine the level of hexazinone in water in support of the degradation kinetics study. The results indicate a limit of detection (LOD) at 0.05 mu g/l and the recoveries between 90.2 and 98.5% with relative standard deviations (RSD) lower than 12%. A LC-MS/MS technique is used to trace the degradation process. Complete degradation is achieved into final products including nontoxic water, carbon dioxide and urea. A probable pathway for the total photocatalytic degradation of hexazinone is proposed. (C) 2012 Elsevier B.V. All rights reserved.