Patients with prostate cancer who receive systemic androgen deprivation therapy (ADT) and local treatments have a high likelihood to experience depression, anxiety and fatigue. The present study aimed to determine the effects of Frankl's group logotherapy sessions on alleviating these symptoms in individuals with moderate- to high-risk prostate cancer who were receiving pelvic radiotherapy. A quasi-experimental study with pretest–post-test was conducted in which 30 patients were assigned either to the experimental (n = 15) or to the control (n = 15) group. The implicated research instruments were as follows: Beck's Depression Inventory, Beck's Anxiety Inventory, Okayama et al.’s Cancer Fatigue Scale and Luthans' Psychological Capital Questionnaire. The results of the ANCOVA showed that logotherapy significantly affected anxiety (F = 42.51, p < 0.001), depression (F = 39.36, p < 0.001), cancer fatigue (F = 16.54, p < 0.001) and psychological capital (F = 39.86, p < 0.001) in the experimental group compared to the control group, indicating that logotherapy sessions with an emphasis on meanings, aims and values of life, when accompanied by peer interaction, can improve mood and function as well as contributing to positive psychological capital in intermediate and high-risk prostate cancer patients during their treatments.