A new type of poly (thionine)/multiwall carbon nanotube/glassy carbon (PTH/MWNTs/GC) electrode was fabricated by electropolymerization thionine onto the surface of MWNTs modified GC electrode. The properties and behaviors of the modified electrode were characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The results show that the high sensitivity and selectivity are mainly caused by the unique carbon surface of the carbon nanotubes and the catalytic activity of thionine. The modified electrode exhibited excellent electrocatalytic behavior to the oxidation of uracil, and was firstly applied to determinate the concentration of uracil for the differential pulse voltammograms. Under the optimum conditions, linear calibration equation was obtained over the uracil concentration range from 1.0 X 10(-5) to 5.5 X 10(-2)M with a correlation coefficient of 0.9978 and a detection limit 2.0 X 10(-7)M (based on S/N = 3) was also gained. The good electrocatalytic response of uracil at PTH/MWNTs/GC electrode suggests that the PTH/MWNTs are an excellent platform for electrochemical biosensing. The modified electrode displays excellent repeatability, stability, and high sensitivity. (c) 2007 Wiley Periodicals, Inc.