Objective:This study aimed to assess the relationship between religiosity and quality of life (QoL) in patients with breast cancer in a Muslim population.Methods:This descriptive-correlational study was conducted in 84 Muslim patients with breast cancer who were admitted to Ahvaz Shafa Hospital, Iran, during 2015. QoL and religiosity were measured with the Short Form-36 questionnaire and Muslim Religiosity questionnaire based on the Glock and Stark model, respectively. Data were analyzed using a software program for descriptive statistics, the Chi-square test, Pearson's correlation, and an independent sample t-test.Results:Most patients had high religiosity (69%) and moderate QoL (46.5%) scores. Total scores and all subscales scores for QoL were significantly higher in patients with high religiosity than patients with moderate religiosity (P < 0.0001). Moreover, a direct correlation was found between religiosity (total and all subscales) and QoL (total and all subscales) (P < 0.0001).Conclusions:A significant relationship was found between religiosity and QoL in patients with breast cancer. Accordingly, care team members, especially midwifery and nursing staff, should pay more attention to religious beliefs among these patients to improve their QoL.