A potentiometric sensor based on 1,4,8,12-tetraazacyclopentadecane (ionophore) for the determination of Ni2+ ion has been developed. The optimum membrane contained 2.5% ionophore, 31.0% poly vinylchloride (PVC), 65.0% dibutyl phthalate (DBP) as a solvent mediator, and 0.5% potassium tetrakis p-chlorophenyl borate (KTpClPB), as a counter ion. The all solid–state contact PVC membrane Ni2+–selective potentiometric membrane electrode exhibited high sensitivity and short response time. This sensor demonstrated a working concentration range of 1.0×10-1-1.0×10-5 mol L-1, with a Nernstian behavior and a response time of 6-7 s. The detection limit of the Ni2+-selective membrane electrode was about 2.8 × 10-5 mol L-1. The PVC membrane Ni2+-selective electrode demonstrated with a correlation coefficient r2=0.9563 and usable within the pH range of 4-9, and the lifetime of the sensor was 5 weeks.