The properties of two types of diamond based electrodes were investigated, namely diamond screen-printed electrode and boron-doped diamond film electrode, in order to compare their performances and to test the possibility of their application for determination of biologically active organic compounds. The optimal conditions for voltammetric determination of the pesticide acifluorfen by differential pulse voltammetry on a boron-doped diamond thin film electrode were found, the pesticide being successfully determined in real water samples in a concentration range of 1.0x10-7 -1.0x10-6 mol L-1 with a limit of detection of 2.35x10-7mol L-1.