It is estimated that globally, millions of adolescents experience mental health problems, especially anxiety and depression. Adolescents with high perceptions of stress often encounter mental issues, have negative thoughts or are dissatisfied with daily life events. This study employed a quasi-experimental design with two groups and repeated measures to test an innovative nursing intervention, the Be Aware of Stress Smartphone Application. This application aims to increase positive thinking and reduce perceived stress among at-risk adolescents aged 13 to 16, and we sought to determine their satisfaction with its usability. The study was conducted with 44 junior high school students from an opportunity expansion high school in Eastern Thailand, who were randomly assigned to experimental and comparison groups (22 each). Data were collected between December 2023 and February 2024 using the General Information Questionnaire, Positive Thinking Test, Perceived Stress Questionnaire, and Satisfaction of Application Usability scale. The outcomes were measured at baseline, after completing the program at week 4, and at week 8 after using the application. The chi-square test and repeated measures analysis of variance were used to analyze the data. The results of this study have important implications for future research. They indicate a significant improvement in positive thinking and a reduction in perceived stress within the experimental group, compared to the comparison group, at weeks 4 and 8. Moreover, the experimental group reported high satisfaction with the application’s usability. These findings suggest that the Be Aware of Stress application is beneficial for community nurses and others to prevent adolescent stress. The study also highlights the need for future research to enhance the application’s functionality and compatibility with various phone operating systems to ensure widespread and effective use.