Pt nanoparticles supported on porous silicon (PSi) flour was synthesized by a simple in-situ redoxreaction between PtCl62−and PSi, in hydrofluoric acid solution. The components and morphologicalproperties of Pt/PSi nanocomposites were investigated by means of scanning electron microscopy, X-raydiffraction spectroscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, cyclicvoltammetry and electrochemical impedance spectroscopy. Pt/PSi nanocomposite in carbon ionic liquidelectrode (CILE) has synergetic effect on the oxidation of morphine and codeine. Simultaneous deter-mination of morphine and codeine were performed using the proposed sensor by means of adsorptivestriping voltammetry. Under the optimum conditions, the oxidation current responses of morphine andcodeine were linear in the concentration range of 0.10–25.0 micro-mol L−1. The detection limits of 30.0 and 20.0 nmol L−1were achieved for morphine and codeine, respectively. The electrochemical sensor hashigh sensitivity toward the analytes with a good reproducibility (due to the high synergetic activity of Ptnanoparticles and good antifouling properties of the ionic liquid). To check the applicability of the sensor,the proposed sensor was used for the simultaneous determination of morphine and codeine in biologicalfluids with satisfactory results.