Understanding the growth behavior of nanocrystals (NCs), especially when heteroatoms are introduced, is very important for the optimization of doping (or alloying) and optoelectronic performances. Here, it is reported on the observation of alloying‐facilitated self‐assembly of MgZnO NCs and the underlying mechanism of alloying concentration‐dependent surface grafting. Using the developed one‐pot thermolysis of Zn and Mg organic salts with the help of oleylamine (OAm) and oleic acid (OA), the Mg ions can be introduced into the ZnO lattice without phase separation with concentrations as high as 20%. Interestingly, with the increase of Mg alloying concentration, the morphologies of the products transform from monodispersed NCs to nanoflowers, and then nanobouquet superstructures, which have quasi‐monocrystal features and obey the oriented attachment rules. According to the analyses of surface functional groups, a mechanism involving concentration‐dependent surface grafting is proposed for such alloying‐facilitated self‐assembly.