Ultrafine Pd nanocrystals were grown on the cobalt phosphide (Co 2 P) decorated Vulcan XC-72 carbon (C/Co 2 P), which is realized by first implementing the corresponding metal precursor and then the further chemical reduction process. The as-synthesized C/Co 2 P/Pd composite was further constructed to form a gas permeable electrode. This electrode can be applied for formaldehyde (HCHO) detection. The results demonstrate that the Co 2 P nanocrystal can significantly improve the sensing performance of the C/Co 2 P/Pd electrode for catalytic oxidation of HCHO, which is considered to be attributed to the effective electron transfer from Co 2 P to Pd in the C/Co 2 P/Pd composites. Furthermore, the assembled C/Co 2 P/Pd sensor exhibits high sensitivity of 617 nA/ppm and good selectivity toward various interfering gases such as NO 2 , NO, SO 2 , CO 2 , and CO. It also shows the excellent linear response that the correlation coefficient is 0.994 in the concentration range of 1-10 ppm. Therefore, the proposed cost-effective C/Co 2 P/Pd nanocomposite, which owns advantages such as high activity and good stability, has the potential to be applied as an effective electrocatalyst for amperometric HCHO detection.