Abstract: An experimental research on PVC matrix membrane TlBr₄^- ion-selective electrode based on the ethyl violet-TlBr₄^- ion pair is described. The electrode exhibits Nernstian response for TlBr₄^- with a slop of 58 mV/decade (25℃) over the concentration range 3.2×10^-3-7.4×10^-7M in pH range from 2 to 6. The practical response time takes one minute. The electrode resistance is about 7 × 1⁰6 Ω. The lifetimes of the electrode keep going over eight months. The potential drift is less than 1.1 mV for four hours. The MnO₄^-, ClO₄^-, IO₄^-, BF₄^-, SCN^- and picrate anions do not show remarkable interference, only anionic complex AuBr₄^- shows interference for this electrode.The electrode has been applied to determination of trace of thallium in the soot by means of modified null-point potentiometry with good results.