Objective: The present study examined the extent to which social support (SS) availability and satisfaction could predict the extent of caregiver burden (CB) among mothers of children with Acute Lymphocytic Leukemia (ALL). Method: The study was a cross-sectional, descriptive-correlative study. It was conducted on a sample of 117 mothers whose children were undergoing treatment in a public hospital in Bam, Iran. The Norbeck Social Support Scale and the Caregiver Burden Scale were used to measuring study variables. The data were analyzed using Pearson's correlations, t-tests, ANOVAs, and linear regressions. Results: Significant correlations were observed between CB and SS availability (r = -0.499, p < 0.001), SS satisfaction (r = -0.543, p < 0.001), the age of the child with cancer (r = -0.22, p = 0.01), and duration of treatment (r = 0.336, p < 0.001). Married mothers experienced less CB than those that were widowed or divorced. Within the regression equation, SS satisfaction, SS availability, marital status, and duration of treatment were the predictors of CB. Significance of results: Based on the results of the current study, mothers who have less SS, especially those who are single mothers, with younger children, and who have taken care of their child for an extended duration should be given special attention. Furthermore, it appears that there are distinct cultural variations amongst Iranian mothers which suggest that culture may impact upon SS availability. Results also suggest a need for interventions that enhance nurses' ability to provide support to caregivers and the broader family unit as a whole. Nurses in cancer care need to have psychological competencies to help family members of cancer patients especially mothers and more so those that are single mothers. As integral members of the patient care experience, nurses may be uniquely positioned to provide this needed psychosocial support.