In the presence of pre-synthesized Au nanoparticles both pulse radiolysis and 2-propanol assisted reduction of Pd (II) chloride to palladium have been investigated with the intention to check the possible formation of Au–Pd heteroaggregates. Pulse radiolysis of Pd 2+ (50Gy dose/pulse at 298K in 270mM 2-propanol to scavange OH radicals) produced Pd nanoparticles of 3.9–2.5nm depending on the citrate concentration (2.8–12×10 −4 M). UV–vis measurements and TEM investigations confirmed that part of the Pd particles were attached to the Au particles of 28±6nm forming Au–Pd heteroaggregates. Hydrothermal treatment of Pd hydrosol at 363–395K in the presence of Au nanoparticles was observed to facilitate formation of Pd tendrils on Au and 2D Pd structures by aggregation process. Reduction of Pd 2+ with 2-propanol (1.55–2.2M) in Au hydrosol and sodium citrate as capping agent was also tested at 348–353K. At pH 3.5–4.5 reduction of Pd 2+ resulted in an effective decoration of the gold particles with small crystals of Pd. The observed structures definitely differ from the usual Au/Pd core/shell nanoparticles. The Pd–Au samples were characterized by UV–vis, transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). Hydrogenation of 1,3-cyclooctadiene in the liquid phase was applied for the additional characterization of the structurally different samples.