The purpose of this study was to explore the relationship between high school students´ codependency and trust. The sample consisted of 1264 students from high schools in Taiwan. The instruments used in this study included The Spann-Fischer Codependency Scale, Codependency Assessment Questionnaire, and Trust Scale. The primary findings were as follows: there were sex differences, grade differences and varied developmental trends in codependency and trust. And the canonical correlational analysis showed that the relationship between codependency and trust was varied. According to the research, teachers or counselors were suggested to pay attention to the sex differences, grade differences and developmental trends in codependency and trust among high school students.