Objective: To analyze the association between social support and mother's anxiety, the category of social support received, needed by mother treating the child with cancer. Method: This study non-experimental approach sequential explanatory mixed method strategy. Analytical correlation cross-sectional study 49 mothers treating the child with cancer in Installing Child Health Hospital Dr. Sardjito selected by consecutive sampling, qualitative exploration 9 informants selected by purposive sampling. The research instrument using Social Support Questionnaire, Pediatric Inventory for Parents, in-depth interview guide. Analysis using Pearson and content analysis. Results: Mother's worried long-term effects of cancer (55, 10%). The correlation number of support persons with mother's anxiety (r = 0.166; p = 0.253), correlation between satisfaction received support with mother's anxiety (r = -0.330; p = 0.021). Findings are mothers who less social support are the risk of severe anxiety, mothers get meaningful support and needed such as information and emotional support from family, neighbors, fellow who had the child with cancer, health workers. Instrumental and appraisal support from families, neighbors, friend, health workers. The mother states information support is important from the health worker, the fellow who had the child with cancer it makes to adapt, accept child's condition, emotional support from family make mother felt more confident treating child's. Conclusion: There is no correlation number of support persons and mother's anxiety. There is a significant negative correlation satisfaction received support and mother's anxiety. Category of support received, needed by mother especially information, emotional support.