Background: The experience of caring for cancer patients has adverse outcomes for family caregivers. The ability to care for a sick child is affected by the mother’s health; to empower mothers, it will be necessary to examine their caring ability. Objective: The aim of this study was to carry out a psychometric evaluation of the Caring Ability of Family Caregivers of Patients With Cancer Scale–Mothers’ Version (CAFCPCS–Mothers’ Version). Methods: The present study is a psychometric evaluation of the CAFCPCS–Mothers’ Version. The sample consisted of 196 mothers of children in treatment for cancer selected through convenience sampling. The face, content and construct validity, internal consistency, and stability of the scale were measured. Data were analyzed using the software SPSS 19 and LISREL 8.8. Results: After removing 2 items during confirmatory factor analysis, the values of root-mean-square error of approximation, comparative fit index, and nonnormed fit index were reported to be 0.066, 0.92, and 0.91, respectively. The Cronbach’s α was calculated to be 0.71 and the stability correlation coefficient was 0.75. The final tested scale included 29 items in 5 dimensions: effective role play, fatigue and surrender, trust, uncertainty, and caring ignorance for mothers of children with cancer. Conclusion: The CAFCPCS–Mothers’ Version has satisfactory content, face, and construct validity and adequate reliability in terms of internal consistency and stability in a sample of mothers of children receiving treatment for cancer. Implication for Practice: The CAFCPCS–Mothers’ Version can be used to assess the caring ability of Iranian mothers of children with cancer and to determine maternal care needs.