Diagnosing cancer, as a life-threatening event, in children and adolescents stops the normal course of life for all family members. Spirituality, which plays an essential role in coping with illness and death, can increase resistance against psychological crises induced by cancer diagnosis and treatment. This study aims to discover the spiritual needs of mothers having children with cancer aged 1-12 years old. In this qualitative study, the conventional content analysis approach was used. The research environment was three pediatric oncology wards of Amir Hospital in Shiraz, Iran. Data were collected from September 2019 to March 2020 through face-to-face semi-structured in-depth interviews. Fifteen participants including 12 mothers and 3 nurses were interviewed through purposive method considering maximal variation. The interviews were recorded, transcribed, and subjected to a qualitative analysis. Credibility, dependability, confirmability, and transferability of data were confirmed. The mean (± standard deviation) age of the mothers was 35.76 (±5.96) years old. The spiritual needs of the mothers were classified into three categories, including religious well-being, existential well-being, and growth and excellence as well as seven subcategories. Religious well-being included subcategories of direct and indirect connection with God, existential well-being included subcategories of need for hope, multifaceted support, and rethinking, growth, and excellence consisted of subcategories of devoting yourself and surrender. Mothers of children with cancer face important spiritual needs. Therefore, it is necessary for the treatment team to identify these needs and use them to provide appropriate spiritual care.