A solid-state ion-selective electrode for detection of tramadol has been fabricated utilizing polyaniline nanoparticles as an ion-to-electron transducer layer. The polyaniline (PANI) nanoparticles were synthesized by the micellar emulsion chemical polymerization method and the mean particle size was similar to 8 nm. The inclusion of PANI nanoparticles as an ion-to-electron transducer layer between an ionophore-doped PVC membrane and solid contact electrodes was carried out to improve the stability of the electrical signal. Both short and long-term stability studies were performed and compared to PANI free electrodes. Furthermore, the electrode's stability at various pH levels was investigated. The formation of water at PANI/solid contact interface was studied. Results indicate an absence of the water layer at the interface. The PANI/solid contact electrodes had good piece-to-piece reproducibility and potential stability over 30 days. The fabricated electrodes were utilized for tramadol determination as a model pharmaceutical drug in the presence of all excipients; the linear range was 10(-6) to 10(-2) mol L-1, pH stability range was from 3-7 and the detection limit was calculated to be 3.9 x 10(-7) mol L-1. (C) 2014 The Electrochemical Society. All rights reserved.