A Eu(III) ion-selective polyvinyl chloride (PVC) membrane sensor based on 1,4-bis[o- (thiophene-2-carboxamidophenyl)]-1,4-dithiobutane as a new nitrogen-, oxygen- and sulfurcontaining sensing material was constructed. The sensor has a Nernstian slope of 19.5 ± 0.6 mV per decade across a wide concentration range between 1.0 × 10-6 and 1.0 × 10-2 M and a detection limit of 6.7 × 10-7 M. In this work, selectivity coefficients were determined by the matched potential method (MPM). The advantage of the sensor is its excellent Eu(III)-selectivity with regard to most common metal ions, and especially, all lanthanide ions. It was used as an indicator electrode in potentiometric titration of 25 mL of a 1.0×10−4 M Eu(III) solution with a 1.0×10−2 M EDTA solution.