The theory of “cognitive dissonance” is one of the many topics related to customer satisfaction research. Some research used “free-choice paradigm” which is known to present threats to people in post-decision. However, most of the experiments focus only on theoretical frameworks, leaving aside consumer decision making. Therefore, this paper aimed to clarify the effect of online reviews on post-decision cognitive dissonance. In the experiment, participants were asked to choose the best item from nine earphones, each one of them had online reviews which were manipulated by an experimenter. When some participants saw some reviews which supported their decision, they justified their choices. In contrast, when some participants saw some reviews which unsupported their decision, they didn't only justify but also showed some unpleasant feelings towards the reviews. To conclude, some consumers were strongly influenced by online reviews after purchase.