A carbon paste electrode (CPE) was modified by incorporation of carbon nanotubes and ferrocene (FC) and studied in pH 7.0 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode showed an excellent electrocatalytic effect on the oxidation of norepinephrine (NE). In PBS of pH 7.0, the oxidation current increased linearly with concentration of NE from 0.47 to 500.0 μmol L⁻¹. The detection limit (3σ) obtained by differential pulse voltammetry (DPV) was 0.21 μmol L⁻¹. Then the modified electrode was used to determine NE in an excess of acetaminophen (AC) and tryptophan (TRP) by DPV. Finally, this method was used for the determination of NE, AC and TRP in some real samples.