Borderline personality traits of mothers impact those in their adolescent children. This study seeks to identify whether adolescent humor mediates this influence and whether a humorous home environment cultivates humor in adolescents. To this end, I conducted a questionnaire urvey of 347 people (96 men and 251 women; M age=20.55, SD=1.30) and conducted a structural equation model based on the results. The higher the mothers' borderline personality traits that adolescents reported, the higher the adolescents' borderline traits that adolescents reported. Positive humor (one subcategory of humor) negatively impacted borderline personality traits of adolescents, while negative humor (the other humor subcategory) positively impacted it. Positive humor and a humorous home environment mediated the levels of maternal and adolescent borderline traits. Negative humor also mediated between them by increasing adolescent borderline traits. This study demonstrated the importance of humor for adolescent children of mothers with borderline personality traits.