Manipulating　the　growth　mode　of　colloidal　nanocrystals　is　of　both　fundamental　interest　and　technological　importance　because　it　is　often　connected　to　the　control　of　their　shape,　morphology,　and　physicochemical　properties.　In　conventional　wisdom,　island　growth　during　thin-film　deposition　is　restricted　to　lattice-mismatched　materials.　Here,　we　show　that　deposition　of　Au　on　Au　nanostructures　(e.g.,　nanoplates,　nanorods,　and　nanospheres)　can　produce　separate　Au　islands　on　the　seed　surface　with　tunable　size　and　density　while　preserving　the　original　crystal　structure.　The　island　growth　in　the　system　is　ascribed　to　the　synergistic　effect　of　fast　redox　kinetics　and　surface　capping　of　large　polymeric　ligands.　Decreasing　the　reaction　rate　or　changing　the　capping　ligands　could　readily　transform　the　deposition　of　Au　on　Au　nanostructures　from　island　growth　to　layer-by-layer　mode.　We　further　take　advantage　of　the　dense　hotspots　of　the　islands-on-plate　nanostructures　and　demonstrate　their　excellence　in　surface-enhanced　Raman　scattering　detection.