Background: Although the life expectancy of many cancer patients has increased due to the increasing progress of medical science today, however, since this disease is still the cause of a high percentage of deaths, it is always accompanied by fears, stress and reduced adaptation. On the other hand, health resources are increasingly highlighting spirituality and its importance in health and illness. Objectives: This research was conducted in order to investigate the effect of existential psychotherapy using the Yalom method using the story therapy approach on the level of anxiety, stress, depression and life expectancy in women with cancer undergoing chemotherapy. Methods: The present study was an experimental study based on pre-test-post-test randomized group design with a control group with a sample of women with cancer undergoing chemotherapy who referred to one of the private clinics in Karaj city in Iran. 24 people were selected by random sampling method after the initial evaluation and were randomly replaced in two groups of 12 people, control and experimental. After that, all the subjects were tested by means of research tools, including Depression-Anxiety-Stress Scale (DASS-21) and Snyder’s Hope Scale (SHS). The people of the experimental group participated in existential group therapy interventions during 8 sessions (tow-hours sessions), while the control group did not receive any intervention. At the end, the tests were conducted again for all 24 people and after collecting the questionnaires, the obtained data were analyzed using SPSS and the statistical test of covariance analysis. Results: The findings indicated that Yalom existential group psychotherapy led to a significant difference between the groups in the level of depression (P < 0.0001), stress (P < 0.0001), anxiety (P < 0.0001) and the level of Life expectancy (P < 0.0001) in women with cancer undergoing chemotherapy was compared to the control group. Conclusions: The obtained results indicate that group psychotherapy using the story therapy approach has been significantly effective in reducing depression, anxiety and stress and increasing the life expectancy of women with cancer undergoing chemotherapy.