Gold nanocrystals and nanoassemblies have attracted extensive attention for various applications, including chemical and biological sensing, solar energy harvesting, and plasmon-enhanced spectroscopies, due to their unique plasmonic properties. It is of great importance to prepare shape-controlled Au nanocrystals with high monodispersity over a large range of sizes. In this work, Au nanospheres with sizes ranging from 20 nm to 220 nm are prepared using a simple seed-mediated growth method aided with mild oxidation. As-prepared Au nanospheres are remarkably uniform in size. The resultant Au nanospheres of different sizes are ideal building blocks for constructing plasmonic nanoassemblies. Core/satellite nanostructures are assembled out of differently sized Au nanospheres with molecular linkers. The core/satellite nanostructures show a red-shifted plasmon resonance peak in comparison to that of the Au cores, which is consistent with the results calculated according to Mie theory. As predicted by finite-difference time-domain simulations, the assembled core/satellite nanostructures exhibit strongly enhance Raman signals. This facile growth of Au nanospheres and assembly of core/satellite nanostructures are expected to facilitate the design of new nanoassemblies with desired plasmonic properties and functions.