RAFT dispersion polymerization following the formulation of polymerization induced self-assembly (PISA) and micellization of pre-prepared amphiphilic block copolymers in block-selective solvents are generally used to prepare block copolymer nano-assemblies. Herein, we make a comparison between these two methods by employing two typical block copolymers of poly(acrylic acid)-block-polystyrene (PAA-b-PS) and poly(ethylene glycol)-block-polystyrene (PEG-b-PS). It is found that the block copolymer nano-assemblies prepared by these two methods are similar with each other when the solvophilic block is relatively long and the solvophobic block is relatively short. Otherwise, the block copolymer nano-assemblies by these two methods are different. The possible reasons leading to the difference between PISA and micellization are discussed, and the kinetic factors including temperature, polymer concentration and solvent are ascribed. It is thought that the present study is helpful to clarify how the kinetic factors beyond the block copolymer itself affecting block copolymer morphology. (C) 2018 Elsevier Ltd. All rights reserved.