Direct Formic Acid Fuel Cells (DFAFCs) have been extensively focused and rapidly growing as one of alternative energy systems for portable devices and automobiles. However, power energy requires the active and selective metal nanocatalysts to perform the highest electrochemical activity. Here, we propose a nanocubic shape of palladium nanoparticles (PdNPs) decorated on functionalized graphene (fG), where surface modification is obtained by surfactant free method. The 11 nm and high dispersion of Pd nanocubes (PdNCs), which are majorly enclosed with (1 0 0) indicated by XRD and HRTEM results, are successfully deposited on functionalized graphene (PdNCs/fG) and used as an enhanced electrocatalysts for formic acid oxidation. Our PdNCs/fG catalyst displays a remarkable mass activity towards formic acid oxidation (494.50 A/g, over 100 times) compared to commercial catalysts of Pd/C, and over 20 times to PdNPs on unmodified graphene or reduced graphene oxide (PdNPs/rGO). Moreover, our catalyst exhibits better stability and higher CO resistance. The PdNCs/fG catalyst also generates the superior specific activity towards formic acid oxidation to 20.37 A/m(2). The study demonstrates the synergistic effect of high selective site enabled by {1 0 0} facet on PdNCs and a great potential from a support of modified graphene to Pd metal catalyst for the development of electrocatalysts in fuel cell applications.