An approach is developed to fabricate supported AuPd nanoparticles (NPs) with high catalytic activity and good separability depending on these amino-modified polymer microspheres (Fe3O4@PS-NH2). After the careful surface modification with amino groups, the selective adsorption of these magnetic polymer carriers to p-nitrophenol (4-NP) is much available for the improvement of the catalytic activity of immobilized AuPd nanoparticles. Furthermore, the catalytic activity of the bimetallic catalyst could be tunable via controlling the surface coverage of palladium on Au nanoparticles. The catalytic activity of supported AuPd NPs (S-AuPd250%) for 4-NP reduction increased 3.78 times compared with that of isolated AuPd NPs. The catalytic activity (k/m(Au)) even reached 479.78min(-1)mg(-1) as S-AuPd150% and was selected as the catalyst. In addition, these supported AuPd nanoparticles are easily and rapidly isolated by magnetic separation. Due to its high stability, these supported AuPd NPs could be recycled for 30 runs without any loss of catalytic activity. Thus, the high catalytic activity and easy separability of this supported AuPd NPs are efficiently combined together, which is showing great potential in nanocatalysts.