Oseltamivir phosphate (OP) is an antiviral drug that is used in the treatment and prophylaxis of both influenza A and influenza B. It is effective against all known influenza viruses that can infect humans, including pandemic influenza viruses and may be the most appropriate antiviral option against avian influenza caused by H5N1 virus. Tamiflu, the registered trademark used under exclusive license by Roche laboratories with OP as active pharmaceutical ingredient, is considered the best treatment for the bird flu disease. The construction and electrochemical response characteristics of poly vinyl chloride (PVC) membrane sensors for the determination of (OP) were described. The sensors are based on the use of the ion association complexes of (OP) cation with sodium tetraphenylborate–oseltamivir phosphate (NaTPB–OP), tungestosilisate–oseltamivir phosphate (TS–OP), phosphomolbdate–oseltamivir phosphate (PM–OP) and phosphotungestate–oseltamivir phosphate (PT–OP) as ion exchange sites in the PVC matrix. The performance characteristics of these sensors, which were evaluated according to IUPAC recommendations, reveal a fast, stable and linear response for (OP) over the concentration range from 10−5 to 10−2 mol L−1 with cationic slopes of 51.5 ± 0.3, 50 ± 0.5, 55 ± 0.2 and 50 ± 0.4 mV per decade across an extended OP concentration range from 1.0 × 10−6 to 1.0 × 10−2 mol L−1 for NaTPB–OP, TS–OP, PM–OP and PT–OP, respectively. The direct potentiometric determination of (OP) using the proposed sensors gave average recoveries of 99.9, 99.8, 99.9 and 99.7 for NaTPB–OP, TS–OP, PM–OP and PT–OP, respectively. The sensors are used for determination of (OP) in tablets. The method was successfully applied to commercial pharmaceuticals, Tamiflu. Validation of the method shows suitability of the proposed sensors for use in the quality control assessment of (OP). The developed method was found to be simple, accurate and precise when compared with a reported HPLC method.