Pd-based anode catalysts with superior activity are urgent for formic acid oxidation to further boost the direct formic acid fuel cells (DFAFCs) technologies. Herein, a strategy of ethylenediamine (EDA) modified Pd/C catalyst was developed by two main steps of EDA adsorbed on Vulcan XC-72 carbon by impregnation and Pd nanoparticles loaded on the freeze-dried C-EDA supports by liquid reduction method. The effects of sweep rates and concentrations of EDA on the formic acid electrooxidation were systematically studied. Results showed that the above parameter was optimized as the concentration of EDA of 0.1 mol L. Pd nanoparticles with even distribution were fabricated and particle sizes were in the range of 3.5–4.2 nm. In addition, Pd particle size became smaller with the addition of EDA, suggesting that EDA could induce the generation of smaller Pd. Electrochemical measurements demonstrated that the electrocatalytic activity of Pd/C-0.22EDA (1021 mA mg) with optimized modification concentration was improved as a factor of 3.82 than that of Pd/C (267 mA mg). An enhanced stability (about 41 times higher than Pd/C) and faster charge-transfer kinetics of formic acid electrooxidation were observed for Pd/C-0.22EDA catalyst. CV and CA measurements showed that the most active catalyst was made of the smallest (3.5 nm) Pd nanoparticles for Pd/C-0.22EDA catalyst. The better electrocatalytic performances of Pd/C-0.22EDA might be ascribed to evenly dispersed Pd with relatively smaller particle size, electron regulation between Pd and amine group as well as stable Pd structure.