The purpose of this study was to examine the relationship among parental conflict perceived by adolescents, irrational belief, and maladjustment behavior(internalizing and externalizing problems) and to investigate the mediating effect of irrational belief in the relationship between parental conflict perceived by adolescents and maladjustment behavior. The subjects of this study were 413(203 male, 210 female) students in the first and second grade of three high schools located at M city in Jeonnam province. The parental conflict scale, maladjustment behavior scale, and irrational belief scale were completed. SPSSWIN 27.0 for Windows was used for descriptive statistics and correlation analysis and SPSS Process Macro 4.0 was used for multiple regression analysis and bootstrapping. First, parental conflict perceived by adolescents showed positive correlation with irrational beliefs, internalization problems, and externalization problems, while irrational beliefs showed positive correlation with internalization problems and externalization problems. Second, irrational beliefs had partial mediating effects between parental conflict perceived by adolescents and internalization problems. Third, irrational beliefs had partial mediating effects between parental conflict perceived by adolescents and externalization problems.