Objective To describe the caring ability of family caregivers of children with cancer. Method This is a descriptive, exploratory study with a quantitative approach. A sample of 85 family caregivers of children with cancer was taken. After a characterization, they respondd to the Caring Ability Inventory adapted for family caregivers of people with chronic non-communicable disease. Results The family caregivers werecharacterized by age, gender, socioeconomic level, education level, family relationship with the care receiver, social support, time of experience, and burden of care generated by the degree of the receiver's illness. The overall caring ability was described, as well as the ability of each dimension, including knowledge, courage, and patience. Conclusions The principal family caregivers of children with cancer were mainly the mothers of the children with cancer. 70.6 % of them do not possess sufficient ability to take care of their children with cancer. 31.8 % of the group had a lower ability level. This finding, together with the demands of coping with the fact of having a child with cancer, can be a great burden to family caregivers and generate risk for the ill children under their care.