Objective: To study the relationship between Psychological Capital and Ethical behavior, and to identify which Psychological Capital components that predicts Ethical behavior in secondary school students.

Materials and Methods: The sample group included 387 students at one Secondary School. The data collection instrument was the questionnaires which consisted of 3 parts; a Student’s general questionnaire, the Thai Psychological Capital Inventory, and the Ethical Behavior Questionnaire. The statistics used to analyze data were frequency, percentage, mean, standard deviation [SD], independent samples t-test, one-way ANOVA, Pearson’s product-moment correlation coefficient and Stepwise multiple regression analysis.

Results: The present study found the levels of Psychological Capital, in Psychological Capital components were moderately high. The results of comparing Ethical behaviors based on gender found female students had higher Ethical behavior than male students with a statistical significance at the 0.001 level and the results of comparing Ethical behavior based on class levels found that students who studied at different class levels did not have different Ethical behavior. In addition, the Psychological Capital and Psychological Capital components were positively related to Ethical behavior at a moderate level with a statistical significance at a the 0.001 level. The Psychological Capital components such as Optimism, Self-efficacy and Resilience could predict the Ethical behavior of secondary school students by 29%. The correlation coefficient is 0.538 and the standard error of estimate is ±7.857.

Conclusion: Psychological Capital was positively related to Ethical behavior and three Psychological Capital components including Optimism, Self-efficacy and Resilience can predict the Ethical behavior of secondary school students by 29%. Therefore, promoting and supporting these components can be a method by which there can be an increase and help develop Ethical behavior in secondary school students.

Keywords: Psychological capital, Ethical behavior, Secondary school student