A new nanocomposite (porous silicon supported Pt–Pd nanoalloy) was prepared and used as an electrodematerial for simultaneous determination of adenine and guanine. For this purpose, Pt–Pd nanoparti-cles were supported on porous silicon microparticles by a simple galvanic reaction in a HF solution.The nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spec-troscopy, X-ray diffraction spectroscopy and cyclic voltammetry. Incorporation of Pt–Pd/porous silicon(Pt–Pd/PSi) nanocomposite in the carbon nanotube paste electrode (CNTPE) increased the oxidation peakcurrents (about 3 folds) and reduced the overpotential of adenine and guanine. The effects of differ-ent parameters such as pH, accumulation time, accumulation potential, and potential scan rate on thesensitivity were investigated. The new developed sensor was then employed for simultaneous determi-nation of purine bases with linear ranges of 0.10–10.0 mol L−1, using differential pulse voltammetry.Detection limits of 30 and 20 nmol L−1were achieved for adenine and guanine, respectively. Individ-ual determination of purine bases were performed by amperometric technique with a linear rangeof 60.0 nmol L−1–55.0 mol L−1and detection limit of 30 nmol L−1for adenine, while the linear rangeof 40.0 nmol L−1–53.4 mol L−1with detection limit of 10 nmol L−1was achieved for guanine. Finally,the proposed electrochemical sensor was employed to determine adenine and guanine in single-stranddeoxyribonucleic acid (ssDNA) samples.