 A nanocomposite of iron(III) oxide and tin(IV) oxide, Fe2O3(0.5)/SnO2(0.5), was prepared by a solid-phase reaction in an alkaline medium. The nanocomposite was characterized by X-ray diffraction, field-emission scanning electron microscopy, and Fourier transform infrared spectroscopy. A fast-response sensor was prepared by electrochemical deposition of the nanocomposite on a glassy carbon electrode. The prepared sensor has an excellent electrocatalytic activity toward the oxidation of epinephrine (EP), acetaminophen (AC), and tryptophan (Trp), therefore, this sensor was used for simultaneous determination of the above drugs. The separation of the oxidation peak potentials for EP–AC and AC–Trp were about 160 and 280 mV, respectively. The calibration curves obtained for EP, AC, and Trp were in the ranges of 0.6–270.0 µmol L−1, 4.5–876.0 µmol L−1, and 0.6–70.0 µmol L−1, respectively. The detection limits (S/N = 3) were 0.07, 0.2, and 0.1 µmol L−1 for EP, AC, and Trp, respectively. Finally, the sensor was used for determination of EP, AC, and Trp in pharmaceutical and biological samples.