Moral values influence people's opinions and reasoning. While people increasingly share and shape each other's opinions in social media, we have limited understanding of how people's moral values play a role in these processes. As a first step to close this literature gap, we conducted two studies to examine the relationships between one's morality and how one's opinions are expressed and changed in social media. Specifically, we explored the potential of using the moral values reflected from an online comment to classify its stance. We also examined how these moral values contribute to the change of one's opinions in online persuasion processes. Our results show that one's morality and viewpoint are connected, and the more similar between the two users' moral values the more persuasion power one carries over the other. In addition, the stronger a user's moral value the more resistant the user is to change their opinion.