Abstract: The liquid-membrane and PVC membrane ion-selective electrodes for filcilin were studied. They are based on the use of tetraphenylborate-filcilin ion pair complex as the active material. The PVC membrane electrode showed Nernstian response in 10^-2～10^-5M filcilin solution over a pH range of 2.3～6.7 with cationic slope of 58 mV/pC. The electrode showed rapid response, good reproducibility and precision. Using direct potentiometric determination, the recovery of pure filcilin was 99.7% and the standard deviation was ±1.8%, the standard deviation of actual determination of samples was ±0.43. The selectivity coefficient of 24 substances was tested, most of them did not interfere.