Individual's attitude toward a certain behavior is changeable and can further change their intention to perform that behavior. A more concrete and positive attitude usually implies high intention and vice versa. When one cannot be sure if that behavior is correct or acceptable by the society, they tend to refer to others' action. Young adults, such as college students, are at a special stage of development. They spend most of their time with their peers and have a strong desire to integrate into the peer groups. Obviously, that makes them give great weight to the opinion from peers, or in the other words, the peers' norms, and are thus easily influenced by their peers. Take HPV vaccination as an example. If young college students find that most of their peers hold a negative attitude toward it, it is reasonable to infer that the acceptance level is low among these students. Likewise, when their perception of peers' attitudes is changed, their attitudes and behavioral intention may be changed as well.  The theory of normative social behavior (TNSB) explores how various social norms are correlated with each other and how they are integrated to influence individuals' behavior eventually. More specifically, social norms have been categorized into two typical types: the descriptive norm and the injunctive norm. The descriptive norm refers to people's perception about the prevalence of a certain behavior. If one believes that most people around him/her already perform that behavior, it is more likely that he/she will perform it as well. Different from the descriptive norm, the injunctive norm indicates the prevalence of a certain behavior. That means individuals may change their behavioral pattern when they perceive a certain behavior as approved (or forbidden) by the group they belong to. Notably, that normative effect works regardless of the perception accuracy. Moreover, according to Bronfenbrenner's ecological model, human behaviors are influenced by multi-level interactive systems, specifically, the Micro-system, Meso-system, Exo-system, and Macro-system. Convenient sampling was used in this study. A total of 69 female college students were recruited. Multi-level regression was conducted. The findings suggest that, in Hong Kong, the university-level perception of the injunctive norm affects college female students' intention to inject HPV vaccine. In other words, when female students believe many other university students hold a positive attitude toward the vaccine, they are more likely to hold a positive attitude as well, and consequently, have higher intention to vaccinate. However, the society-level normative factors do not matter here. Additionally, the perceived susceptibility also has significant influence on college students' intention.  To conclude, this pilot study investigated the role of social norms on college students' health-related behaviors. The findings roughly supported the theory of normative social behavior and may provide some insights to researchers who are interested in health communication.