Photocatalytic degradation of chlorpyrifos and diazinon, which are extensively used as an organophosphorous pesticide in the agriculture field, has been investigated with UV-radiated TiO$_2$ in aqueous phase. Photodegradation rate was increased with increasing pH of the solution. The removal efficiencies of chlorpyrifos and diazinon were 100% after 200 min in pH 9. Photodegradation followed a pseudo-first-order reaction. The rate constants of chlorpyrifos and diazinon were 0.0160min$^$-1/ and 0.0180min$^$-1/, respectively. NO$_3$$^$-/, PO$_4$$^$3-/, SO$_4$$^$2-/ and Cl$^$-/ were found as end products on the photocatalytic degradation of chlorpyrifos and diazinon with TiO$_2$/UV.