Family caregivers of older cancer patients face many challenges in managing illness. The burden impacts physical, emotional, spiritual, and social health. The objective of this study was to identify burden among caregivers of older patients with advanced cancer, and associated factors. Materials and Methods: Caregivers of older cancer patients were randomly interviewed from March-September 2012. Information on baseline characteristics and caregiver burden using the Zarit Burden Inventory (ZBI) was collected. Descriptive statistics were used to analyze baseline data, with univariate and multiple linear regression to analyze factors associated with higher burden. Results: One hundred and fifty participants were assessed. The mean ZBI was $19.2{pm}12.9$ (95%CI, 17.1, 21.2). Two-thirds of caregivers reported no burden (63%) and the main impact variable on ZBI was guilt. High burdens were associated with single caregiver, relationship with the patient as siblings, presence of migraines, and cancer types of the patients. Conclusions: Caregiver burden of Thai cancer patients is low. This unexpected small number could be the result of the socio-cultural viewpoint. Assessment of caregivers and focusing on related factors should be incorporated into treatment plans.