In this study. we demonstrate the synthesis of carbon nanotubes (CNTs) on clay mineral layers, and the preparation of hydrogen peroxide (H2O2) sensor based on CNT/Nafion/Na-montmorillonite (Clay) composite film for the detection of H2O2. The nickel oxide metallic catalyst (NiO) has been prepared by the polyol method and then dispersed onto the clay mineral layers. The CNTs were successfully synthesized over the NiO/Clay catalyst onto clay layers to form a three-dimensional CNT/Clay network by thermal chemical vapor deposition method. From field-emission scanning electron microscope images, the results of X-ray diffraction and Fourier transfer infrared spectra; the layered clay platelets are apparently delaminated and exfoliated after the growth of CNTs onto the surface of clay minerals. The mixed hybrid film of Nafion and CNT/Clay is coated on the glassy carbon electrode to detect hydrogen peroxide (H2O2). This composite film performs a detection limit of 1.0 X 10(-4) M for H2O2 and the current is linear for H2O2 concentrations from 0.1 to 12.8 mM. Furthermore, the sensitivity of the GCE modified with the CNT/Clay/Nafion hybrid film to H2O2 was calculated to be 1.71 X 10(5) mu AM(-1) cm(-2). Consequently, the CNT/Clay/Nafion medium can probably be a useful electrode for the development of sensors due to its high sensitivity and applicability. (C) 2008 Elsevier B.V. All rights reserved.