The chain extension using bisoxazolines (00) as coupling agent was studied by means of the Monte Carlo (MC) method, focusing on the reaction kinetics. A comparison between simulated results and those calculated by an improved kinetic model was made. The coupling efficiency of the chain extender, average molecular weight and molecular weight distributions (MWDs) were investigated. The results show that the biggest coupling efficiency, the highest average molecular weight and the narrowest MWDs can be obtained when the initial concentrations of carboxyl and oxazoline groups are equal. The results indicate that higher activity difference between the oxazoline group in 00 and that in blocked CA can lead to hi-her average molecular weight and narrower MWDs. Those results are in good agreement with the experiments. Besides above factors, diffusion effect and degradation effect are important factors for the average molecule weight and MWDs. And lower reaction kinetics constants of diffusion effect and degradation effect both result in a higher number-average molecular weight ((M) over bar (n)). The results also indicate that two peaks, at the different molecular weight, appear in the Curve of molecular weight distributions during chain extension reaction. The variation of these two peaks corresponds to different polydispersities. (c) 2005 Elsevier Ltd. All rights reserved.