Objective: to analyze the relationship between the characteristics of patients in cancer treatment, their family caregivers, the care provided with the overload, as well as between overload and the care skills. Method: a cross-sectional study conducted at the chemotherapy and radiotherapy services of a university hospital in Rio Grande do Sul (Brazil) from March to August 2017, with 132 family caregivers of patients in cancer treatment. Data was collected by an instrument that characterizes patients, caregivers and care (the Brazilian version of the Caring Ability Inventory) and the Zarit Overload Scale. The following coefficients were used: Spearman correlation, Mann-Whitney or Kruskal-Wallis. Results: there was a significant relationship between the total overload and the patient’s level of dependence (p=0.021) and help from others (p=0.009). The “care impact” factor was significantly related with the patient’s level of dependence (p=0.006), the caregiver’s gender (p=0.035) and the care help (p=0.043). Regarding the “perception of self-efficacy” factor, there was a significant relationship involving the caregiver’s age (p=0.036) and, in the “caregiver expectation” factor, a significant relationship was observed with the care help (p=0.002). There was a significant and negative correlation between the total care skill and the overload factor related to interpersonal relationship (p=0.035); and between the “courage” dimension and the “perception of self-efficacy” (p=0.032) and “interpersonal relationship” (p=0.008) factors. Conclusion: the characteristics of the patient, the caregiver and the care provided influence the overload of the family caregiver, and this overload, in turn, interferes with the care skills. These results should be considered when planning interventions that aim to guide and prepare family caregivers for home care.