Background: Posttraumatic growth resulting from a stressful factor such as the diagnosis and treatment of cancer can positively affect various aspects of a mother’s life as the child’s main caregiver. The present study aims to determine the level of posttraumatic growth in the mothers of the children with cancer.Methods: In the present descriptive study, the statistical population consisted of the mothers of the children with cancer referring to oncology clinics or hospitalized in the oncology departments of selected hospitals from June 2016 to October 2016. The samples included 180 eligible mothers selected by convenient sampling. The data were collected using “Posttraumatic Growth Inventory” (PTGI) that determines the psychological growth following exposure to traumatic events with 21 items in 5 domains of new possibilities, relationship with others, appreciation of life, personal strength, and spiritual changes and scored by 6-point Likert scale, ranging from 0 to 105; the higher scores indicate greater growth. The data were analyzed in SPSS-20 using descriptive and inferential statistical tests.Results: The mean age of the participating mothers was 34±5.3, 83.3% of whom were housewives. The majority of the children suffered from leukemia, and cancer onset age was between 3 and 6 in 33.9% of the children. The mothers’ mean score of posttraumatic growth was 62.4±18.9, and the highest percentage of scores in various dimensions belonged to “spiritual change” (3.59), “appreciation of life” (3.04), and “relating to others” (3.02).Conclusion: Results showed that the experience of having a child with cancer can lead to posttraumatic growth in mothers.