We report the synthesis and characterization of a group of carboxyl-functionalized poly(amidoamine) (PAMAM) dendrimers of generation 3 (G3) that were used for the stabilization of superparamagnetic iron oxide (Fe₃O₄) nanoparticles (NPs). Folic acid (FA) molecules were conjugated onto the dendrimer surfaces in an attempt to achieve specific targeted imaging of tumor cells that overexpress FA receptors using dendrimer-stabilized Fe₃O₄ NPs. Fe₃O₄ NPs were synthesized using controlled co-precipitation of Fe(II) and Fe(III) ions and the formed dendrimer-stabilized Fe₃O₄ NPs were characterized using transmission electron microscopy (TEM) and polyacrylamide gel electrophoresis (PAGE). The intracellular uptake of dendrimer-stabilized Fe₃O₄ NPs was tested in vitro using KB cells (a human epithelial carcinoma cell line) that overexpress FA receptors. It appears that carboxyl-terminated PAMAM dendrimer-stabilized Fe₃O₄ NPs can be uptaken by KB cells regardless of the repelling force between the negatively charged cells and the negatively charged particles. In the presence of a large amount of carboxyl terminal groups on the dendrimer surface, the receptor-mediated endocytosis of Fe₃O₄ NPs stabilized by FA-modified dendrimers was not facilitated. It implies that the surface charge of dendrimer-stabilized magnetic iron oxide NPs in biological medium is an important factor influencing their biological performance.