The present study aimed to examine whether the psycho-social characteristics were different according to the bystanders' role types (follower, outsider, defender), by focusing on the importance of the bystanders' role as a mediator for the effective bullying prevention and proactive intervention. In order to understand the mechanism of bystanders' behaviors, we also explored structural relations among perceived parenting styles (rejection, overprotection, emotional warmth), character strengths (humanity, courage, justice), and bystanders' behaviors (follow, look on, defense). One-way ANOVA, Scheffé post-hoc test, and Structural Equation Modeling (SEM) analysis were conducted using the data collected from self-reported questionnaires that were given out to a total of 1,005 boys and girls in grade 1 through 3, from 34 classes of 17 middle schools located in Seoul, Gyeonggi-do, and Incheon. The results showed that perceived parenting styles and the character strengths of all virtues showed significant differences according to the bystanders' role types. Moreover, rejective, overprotective, and affectionate parenting styles statically predicted followers' behavior, outsiders' behavior, and defenders' behavior respectively, and overprotective and affectionate parenting statically predicted the children's character strengths manifestation. Meanwhile, rejective parenting did not predict it. Also, the character strengths predicted followers' and outsiders' behavior negatively, and defenders' behavior statically. As a result of analysis of mediating effects, character strengths were found to partially mediate the relationship both `overprotection-look on' and `emotional warmth-defense', excluding `rejection-follow'; thus proving the influence of character strengths. This study suggests that the improvement in parents' parenting styles and the development and utilization of the character strengths will contribute to the reduction of looking on and following behavior in bullying situations and the promotion of defending behavior. In addition, it holds its significance by suggesting the necessity of individualization strategy according to the bystanders' role types, as well as the basis for the importance of parent education.