Social norms have been of interest during recent years due to their influence on human society and people's behavior. This paper studies the effect of social norms on human behaviors through a revised Dictator Game with three different settings, where different social norms are implied. We did find some evidence that social norms have influence on dictators' offering behavior. Dictators tend to offer more when they are facing a social norm which requires them to do so. We also raise possible explanations of this influence through a psychological cost mechanism, which implies that people suffer disutility when they act differently from social norms.