Anisotropic nanoparticles, giving rise to a large number of novel physicochemical properties and functionalities, have provoked increasing attentions in nanoscience and nanotechnology. The remained challenge is to develop synthetic methods for the fabrication of anisotropic nanoparticles with less symmetry under the principle of minimum surface free energy. Here, we established a crystallization-assisted asymmetric assembly method for the synthesis of anisotropic polymer nanocrescents and their carbonaceous analogues by using triblock copolymer F127 and octadecanol in aqueous solution. With the aid of molecular dynamics (MD) simulation, we demonstrate that the observed crescent structure is caused by asymmetry distribution of octadecanol crystal within the hydrophobic core of F127 micelles, via the formation of intermediate elliptic micelles bearing hydrophobic ends that further fuse with each other end-to-end at an angle into curing nanocrescent morphology. The influences of annealing time, annealing temperature, and mole ratios of precursors that govern the kinetics of the assembly and polymerization process were systematically investigated and a series of polymer nanocrescents with tunable length of ~ 85 to ~ 262 nm and aspect ratio of ~ 1.1 to ~ 3.0 were prepared. The ability to create novel crescent-shaped polymer and carbon nanoparticles and the identification of asymmetric assembly process by combining experiment and simulation study will provide a valuable contribution both to theoretical and technological researches.