In middle age, some people may become mentally or emotionally unstable. Additionally, in Japan, mood disorders, such as depressive symptoms, occur mostly among middle-aged women (i.e., aged 40-49 years). However, few studies have examined stressors related to mental health. In the present study, we developed a stressor scale for middle-aged women and examined stressors correlated with middle-aged women's mental health. In January 2015, an anonymous, self-administered survey was mailed to 1,000 randomly selected women aged 45 through 64 years living in Tokyo, Japan. Completed questionnaires were obtained from 329 women (32.9 percent). Factor analysis identified the following stressor categories: "relationship with my husband," "uneasiness about old age," "health concerns," "work-life balance," and "relationship with my friends." "Uneasiness about old age" and "health concerns" were correlated negatively with participants' mental health. Improving middle-aged women's health requires interventions that relieve stressors resulting from age-related problems and promote a positive image of old age.