Gold nanoparticles have great potential in biomedical applications as both a therapeutic and diagnostic agents. Pamam dendrimers are spherical, highly branched macromolecules with a narrow polydispersity to encapsulate and stabilize metal nanoparticles. In the preparation of metal nanoparticles, stabilizers play an important role in controlling particle size. The objectives of this study were to synthesize and characterize of gold nanoparticles. The gold nanoparticles were prepared by reduction of tetrachloroauric acid using sodium borohydride with and without addition of pamam generation 4 dendrimer as stabilizing agent. Gold nanoparticles stabilized pamam generation 4 dendrimer were characterized by Uv‐Vis spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zetasizer. The result showed that UV–vis absorption spectra of gold nanoparticles without pamam G4 dendrimer at 530 nm while absorption spectra of gold–pamam G4 dendrimer at 280 nm. The absorbance peak at 280 nm related to individual of gold nanoparticle encapsulated pamam dendrimer. TEM analysis exhibits the occurrence aggregation of gold nanoparticles without pamam G4 dendrimer. DLS analysis exhibit gold nanoparticles has a particles size 88‐252 nm while gold‐pamam G4 dendrimer nanoparticles 2‐15 nm. The addition of pamam generation 4 dendrimer on preparation of gold nanoparticles could prevent aggregation of nanoparticles through entrapment in cavity or core molecules. Au‐PAMAM G4 nanoparticles 0.1 mg/ml has a greater Hounsfield unit (HU) value than iodine at the same concentration, so it has better contrast properties.