Purpose: This study aimed to assess the burden of care and its relationship with sleep quality of cancer patients’ caregivers.Methods: This descriptive-correlational study was conducted in a referral center of cancer in Zanjan, northwest of Iran. 135 caregivers of cancer patients were recruited through convenience sampling method. The data were collected using a demographic characteristics questionnaire, Novak and Guest’s caregiver burden inventory and Pittsburgh sleep quality index (PSQI). The collected data was analyzed using descriptive and inferential statistics.Results: The mean (± SD) age of the participants was 39.71 (± 10.74) years. The mean (± SD) burden of care and sleep quality of the participants was 45.22 (± 17.75) and 8.88 (± 4.21), respectively. It was found that there is a significant positive relationship between burden of care and quality of sleep scores (r = 0.65, P < 0.001).Conclusion: cancer patients’ caregivers endure a remarkable burden of care and their sleep quality is undesirable. Results indicated that an increase in the burden of care reduces the caregiver’s quality of sleep. High burden of care and poor sleep quality may reduce the quality of the provided care that increase the costs and weakens the disease prognosis. According to the study results, reducing burden of care is an effective strategy regarding improving the caregivers’ quality of sleep that can improve the quality of provided cares by caregivers.