The prevalence of suicide is high in patients with prostate cancer. The hypothalamic– pituitary–adrenal (HPA) axis disorder plays a role in the pathophysiology of depression and suicidal ideation. Acupuncture regulates cortisol secretion through controlling the activity of HPA axis. The purpose of this study was to evaluate the effectiveness of acupuncture on decreasing depression, suicidal ideation, and cortisol secretion in a patient with prostate cancer. In a single-case experimental study, lasting from December 2015 to June 2016, a patient suffering from prostate carcinoma with dysthymic disorder and suicidal ideation was selected through purposive sampling method. Following 30 days of evaluation at baseline, the subject was treated for four weeks with auricular acupuncture along with the usual treatment. The results were analyzed by generalized estimation equation (GEE) and Repeated Measures Correlation (rmcorr) through statistical package for the social sciences (SPSS) software version 22. The primary outcomes showed that acupuncture had a significant effect on reducing depression index, suicidal ideation, and cortisol levels during the treatment process (all P values< 0.05). Secondary outcomes further showed that a significant positive correlation existed between depression, suicidal ideation, and salivary cortisol levels (all P values < 0.05). The findings of this study showed that auricular acupuncture can replace medication and psychotherapy to reduce depression and suicidal ideation and regulate HPA-axis function through modulating the cortisol secretion. However, this conclusion requires more high-quality randomized clinical trials.