Abstract: With the continuous development of e-commerce, online word-of-mouth has become an important channel for consumers to know the product information. In recent years, in order to improve the quality of online comments, the e-commerce platforms have launched the function of additional comments one after another. By making use of the real data obtained from the “AutoHome” platform and adopting the research method of natural experiment, this paper explores the impacts of additional comments function on the users' behavior of both the supply and demand sides for the word-of-mouth from the perspectives of both readers and reviewers. The results show that for the readers, the additional comments function can improve readers' perceived usefulness of the comments, so as to reduce their time costs spent in searching of the useful information; and for the authors, the additional comments function can stimulate the enthusiasm of the reviewers to make comments, urging them to write more objective comments. On the whole, the introduction of the additional comments function can optimize the traditional commenting system. The conclusion of this study has not only enriched the theoretical researches in the field of online comments, but also provided decision references for the online WOM platforms to improve the commenting function.

Key words: online word-of-mouth, additional comments, natural experiment, reader perspective, reviewer perspective