Dendrimers have already been successfully used in nanoparticle (NP) catalysis for many years, particularly for Pd NP protection towards carbon-carbon coupling reactions. In this paper, assemblies between Pd nanoparticles and two generations of "click" dendrimers, with 27 (dendrimer-1) and 81 (dendrimer-2) triethylene glycol (TEG) termini, respectively, are examined for catalytic peroxidase-like oxidative activity. This catalysis is investigated with o-phenylenediamine (OPD) and H2O2 as the substrates in water, displaying different colours. The dendritic effect is negative upon increasing generation, i.e., dendrimer 1-Pd nanoparticles show the best results, providing values with a V-max of 1.49 x 10(-9) M s(-1) and K-m of 3.02 mM as obtained with the Michaelis-Menten model. The detection limit is 0.5 mu M of H2O2 detection with dendrimer-1-PdNPs, and both dendrimer-Pd nanocatalysts exhibit excellent robustness of catalytic activity, with a water-dispersive state being stable for at least 2 months, thus showing promise as a mimic for peroxidase catalysts.