Objective We developed a fully automated smartphone-based stress management application and explored its usability, potential feasibility, and preliminary efficacy for stress management in Korean employees. Methods: Healthy employees working in large public enterprises were enrolled. Participants used our automated stress management application for four weeks. With the application, they monitored their stress level and life style factors. Personalized stress management techniques, including psychoeducation and cognitive behavioral technique, were also provided based on their stress level and lifestyle pattern. In 2014, additional relaxation techniques were incorporated. Participants’ mental health status and lifestyle pattern were self-assessed at baseline and at 4 weeks after using the application. Results: A total of 68 subjects were recruited. The application generally received high satisfaction rating. After the intervention, perceived stress level was significantly decreased, both in 2013 and 2014 (BEPSI-K score pre. vs. post. 14.27 vs. 11.00, F=12.49, p=0.001 in 2013; 12.05 vs. 10.00, F=17.18, p<0.001). In 2014, depression symptom severity was also significantly decreased (CES-D score pre- vs. Post-, 17.66 vs. 11.95, F=9.76, p=0.004). The effects were more significant in females and in those <35 years. Conclusion: Our fully automated stress management application is acceptable and usable, showing preliminary efficacy for reducing employees’ stress levels.