Organic ammonium(I) ion selective PVC membrane electrodes based on crown ether-phosphotungstic acid (PW) precipitates, e.g. 18-crown-6-PW, dibenzo-18-crown-6-PW, 15-crown-5-PW, monobenzo-15-crown-5-PW and 12-crown-4-PW, as neutral carriers were developed. Among these crown ether electrodes, the electrodes based on 18-crown-6-PW gave the best performance and exhibited good linear responses with near-Nernstian slopes (ca. 55-63 mV decade - 1 ) for organic ammonium ions, e.g. BuNH + 3 , C 6 H 5 CH 2 NH + 3 , Et 2 NH + 2 and Et 3 NH + , within the concentration range 10 - 1 -10 - 5 M. The electrodes based on 18-crown-6-PW exhibited good selectivity for organic ammonium ions relative to ammonium ion (NH + 4 ), alkali, alkaline earth and some transition metal ions. The electrode performance also depends on the pH of the test solution and the optimum pH range was about ca. 2-6. The effects of concentrations of internal solutions in the electrodes and the composition of electrode membranes were investigated.