Amorphous zinc oxide-silica (a-ZnO-SiO2) nanocomposite has been synthesized using a sol-gel process. X-ray diffraction patterns show a broad diffraction peak of amorphous SiO2 with no peaks related to ZnO wurtzite structure. ZnO-SiO2 nanocomposite posses uniformly spherical particles and large surface area 462 m(2)/g. The prepared a-ZnO-SiO2 nanocomposite was used as a chemical sensor to detect phenyl hydrazine via a simple electrochemical technique by measuring the current-potential (I-V) characteristics. The calibration curve exhibits good linearity over all concentration range from 390 mu M to 50 mM (r(2)= 0.9986) and the limit of detection was estimated to be 1.42 mu M. The sensitivity was calculated to be 10.80 mu A cm(-2) mM(-1) as a result of good adsorption ability and large surface area of the prepared sensor. Interestingly, the modified ZnO-SiO2 nanocomposite sensor electrode was extremely stable during the sensing runs, since no significant sensitivity decrease was observed after being re-used for five times. Furthermore, no deterioration in the I-V characteristics was detected after being stored in ambient conditions for three months, indicating the fabricated sensor exhibited long term stability. (C) 2015 Elsevier B.V. All rights reserved.