New potentiometric sensitive and selective modified screen printed electrodes (MSPE) which based on phosphotungestic acid (PTA), sodium tetraphenyl borate (NaTPB), phosphomolybdic acid (PMA) or ammonium reineckate (RN) ion pairing agents for determination of oxybutynine hydrochloride (OBCH) were developed. The proposed electrodes have Nernstian slope values of 59.20±0.52, 58.00±0.22 and 58.52±0.22 mV decade-1 for electrodes modified with 7.5, 17.5 and 7.5 mg of RN (electrode I), NaTPB (electrode II) and PTA (electrode III) ion pairing agents, respectively. It is found that the dynamic drug concentration range at 25 (C was 1.0x10-5 - 1.0x10-2 mole L-1 with detection limit (LOD) equal 1.0× 10-5 mol L-1 and limit of quantification (LOQ) equal 3.33×10-5 mol L-1. The response of MSPEs was pH independent in the range 2.0-6.0. The investigated electrodes have fast response time of 10, 9 and 8 s for electrodes I, II and III, respectively. These electrodes have good Nernstian response in the temperature range 10–60 °C. The slope of the straight–line obtained represented the isothermal coefficient of MSPEs which were found to be 1.594 ×10-3, 2.151×10-3 and 2.377×10-3 V/ for electrodes I, II and III, respectively. The small values of the isothermal coefficient indicated the high thermal stability of the electrodes. The MSPEs showed a relatively long life time of 36 days. Pure, biological fluids and pharmaceutical formulation of OBCH were quantified using calibration and standard addition methods and the obtained results agreed with that of the official HPLC method. Validation parameters were optimized according to ICH recommendations.