Glucose oxidase was encapsulated in carbon-nanotube/Nafion film modified glass carbon electrode and was used as electrochermiluminescence (ECL) biosensor for glucose. The glucose oxidase can be fixed firmly in the Nation film and carbon nanotubes offer excellent electrocatalytic activity toward luminol and hydrogen peroxide liberated in enzymatic reaction between glucose oxidase and glucose, which would enable sensitive determination of glucose. Under the optimum condition, the linear response range of glucose was found to be 5.0 x 10(-6) to 8.0 X 10(-4) mol/L, and the detection limit (defined as the concentration that could be detected at the signal-to-noise ratio of 3) was 2.0 x 10(-6) mol/L. The present carbon-nanotube/Nafion biocomposite glucose oxidase ECL biosensor showed excellent properties for sensitive determination for glucose with good reproducibility and stability, and it has been used to determine the glucose concentrations in real serum samples with the satisfactory results. (c) 2007 Elsevier Ltd. All rights reserved.