Objective To examine the experience of clinical nurses who participate in a specialty nurse training program as a mentor and to provide reference for the training of nurse mentors. Methods Phenomenological interview study was conducted on 15 nurse mentors in a specialty nurse training program. The interview outline was developed based on the stress process model. Data were analyzed by using Colaizzi′s phenomenological methodology. Results Four main themes (stress and challenge, optimistic evaluation, positive coping, and many benefits/gains) and 16 sub-themes were identified. Conclusion Clinical nurse teachers experience different levels of stress, however,the degree of stress might be alleviated by their self-cognitive evaluation and social support, and then they experience gains. In order to enhance training quality of specialty nurses, it is suggested to strengthen nurse teacher training, reasonably arrange nurse trainees, and protect the rights of nurse teachers to promote their mentoring experience.