Kinetic photodegradation of imazethapyr, a herbicide from imidazolinone class of pesticides, has been investigated in aqueous solution using slurry titanium dioxide (TiO2) and supported on Ahlstrom paper (flexible photocatalytic support). Two types of TiO2 e.g., Millennium PC500 (100% anatase) and Degussa P25 (80% anatase, 20% rutile) were used. Experiments were investigated to evaluate the effect of the adsorption, initial concentrations of the pesticide as well as catalyst doses on the photocatalytic degradation of imazethapyr. Kinetic parameters were experimentally determined and a half-order kinetic was observed. Regarding Langmuir-Hinshelwood model, the kinetic of the imazethapyr degradation was more efficient at higher pesticide concentrations and catalyst doses. Accordingly, Degussa P25 shows higher photocatalytic activity in regard to PC500 Millennium.