Defense mechanism is an unconscious method for humans to protect themselves from uncomfortable situations when the situations seem to cause trouble to the human mind. One novel that contains a character who unconsciously applies defense mechanisms in daily life to avoid conflict is Fangirl by Rainbow Rowell. It tells about Cather Avery and her journey to adapt to a new environment as she is an introvert and has a problem socializing with her surroundings. This research aims to analyze how defense mechanisms are portrayed by Cather as the main character in the novel and used defense mechanism theory by Sigmund Freud along with characterization and the tripartite of human psyche theory as supportive theories to identify each defense mechanism portrayed by the main character. In this research, the researcher used qualitative research with a psychological approach. Based on the analysis, the researcher found out that the main character used reaction formation, projection, denial, regression, acting out, intellectualization, rationalization, repression, and displacement whenever she felt uncomfortable with her surroundings. In every defense mechanism Cather portrays, she has her own reason to apply it without a second thought unconsciously as she avoids making herself trapped in uncomfortable situations that were mainly triggered by her mom, which caused Cather to feel anxious most of the time.