As a social being, people can cooperate and control one another through the power of reputation, which is a critical opinion of someone given by others. Nevertheless, there have been obstacles in clarifying the identity of traditional types of reputation, for they are mostly words of mouth passed among members of a society. However, due to dramatic technological advancement and widespread use of the Internet and social media, now we can clearly see and analyze written reputations, which used to be passed only from mouth to mouth.Against this background, this study examines whether a negativity bias-a notion that an event of a more negative nature has a greater effect on one's psychological state than a positive event-applies to spread of reputation online, and examines related factors and effects. To this end, reputation-related online comments left by social media users during the election period of Korea's 6th provincial election on 4 June 2014 were analyzed. For the analysis, a Bass diffusion model was used, which is based on the innovation diffusion theory.The analysis results confirmed that, at online forum, negative reputations spread more quickly and more widely than positive ones, had a greater impact, and mass media such as online news outlets had a significant influence on spread of reputation online.