This study examined the effect of valence for best reply on the conformity of general reply in online environment. A total of 194 participants participated in this study, each participant assigned randomly in three experimental groups(positive, negative, and control). Participants were asked to read online news article, best reply and general 6 replies, and then, to write their own opinions in the reply section. In addition, the level of self-expression and issue commitment were measured. The contents of reply participants written was categorized three valence(positive, negative, and neutral) by the four experimenters' judgment. The mean of inter-rater reliability was 84.9%. The results indicated that the level of self-expression and issue commitment were comparable across experimental conditions. However, the result of cross-table analysis showed that there is a significant difference in the valence of general reply across experimental conditions. Specifically, there were significant difference in the valence of general reply between positive and negative experimental group and positive and control group, but there is no significant difference between negative and control group.