Introduction. In Korea, high school students are very low in happiness because they possess many worries about better university entrance and career development. The purpose of this study was to focus on increasing happiness by examining whether the growth mindset moderates the dual mediating effects of mindfulness and hope between gratitude and happiness. Study participants and methods. The participants of this research were male (50.6%) and female (49.4%) among 435 high school students, and 86.2% of the participants lived in small and medium-sized cities, Dong and Eup. As for parental occupations, sales, service, and production jobs accounted for the most, at 32.2%. The household income level was medium for 51.0% of the participants, and 64.1% had dual-income parents. The SPSS Win. 25 and the PROCESS macro 3.5. were used for data analysis. Descriptive statistical analysis, reliability analysis, mean comparison analysis, and moderated mediation effect analysis were conducted. Results. First, there was significant positive correlation between all of the variables. Gratitude and happiness had the highest correlation coefficient (r=.494, p<.01), followed by mindfulness and happiness (r=.452, p<.01), and then gratitude and happiness (r=.451, p<.01). Second, the growth mindset moderates the relationship between gratitude and mindfulness. Third, the growth mindset played a moderated mediating role in the path of gratitude → mindfulness → happiness in both the M and M+SD conditions. Fourth, the growth mindset played a moderated mediating role in the path of gratitude → hope → happiness. Fifth, the growth mindset played a moderated mediating role in the path of gratitude → mindfulness → hope → happiness in M and M+SD conditions. Practical significance. These results will contribute to developing a model to increase happiness by using growth mindset in high school students.