The properties of uranium-sensitive electrodes based on membranes containing uranium di-(4-octylphenyl)phosphate as sensor have been determined, in presence of different phosphates as mediators. The electrode prepared from tritolyl phosphate as mediator was found to give a response of 30 mV/decade over a range of uranium concentration. Interference by Sr(2+), Ba(2+), Ca(2+) and F(-) was also studied, by the mixed solution method. Fluoride interferes severely, by complexation of the UO(2+)(2) ion.