The kinetics of stepwise polymerization in the diffusion-controlled regime was investigated using dynamic Monte Carlo simulation and scaling analysis. In analogy to Flory's expression, a concise expression of reaction kinetics in diffusion controlled regime was proposed, where the number average degree of polymerization was related to the initial concentration and reaction time through a power law dependence. In addition, the transition of kinetics from the classical reaction-controlled to diffusion-controlled regime was predicted and examined via simulation. The results provided a good description of kinetics for the late stage of stepwise polymerizations, and demonstrated good agreements with the various experiments. (C) 2016 Elsevier Ltd. All rights reserved.