The roughened silver–palladium (Pd/Ag(r)) electrode was fabricated by a convenient metallic replacement reaction, and its electrocatalytic property towards reductive dechlorination of 2,4-Dichlorophenoxyacetic acid (2,4-D) in basic aqueous solution have been evaluated. Experimental evidence is presented that Pd/Ag(r) exhibited powerful electrocatalytic activity for dechlorination of 2,4-D. In addition, a new dechlorination mechanism of 2,4-D was proposed, in which the formation of adsorbed 2,4-D on Ag is a key step.