Background: Depression among informal caregivers of cancer patients is the most common and serious medical illness around the world. Caregivers of cancer patients are at greater risk of developing depression than the general population. Informal caregivers’ depression is a global concern that must be addressed early to prevent or decrease its detrimental consequences. Objective: The study aims to assess depression among informal caregivers of patients with cancer at a selected hospital in Bangladesh. Methods: A descriptive cross-sectional study was conducted among 112 informal caregivers of patients with cancer who were selected from the National Institute of Cancer Research and Hospital (NICRH) by using a convenience sampling technique. Data was collected by using self-administered questionnaires from February to March 2023. After data collection, it was analyzed by using descriptive and inferential statistics. Results: The study result revealed that most (91.1%) of the informal caregivers experienced depression. Caregivers’ gender, level of education, occupation, monthly income, place of residence, duration of caregiving, per day caregiving duration, number of children, relationship with the patient, patients’ duration of illness, duration of taking treatment and the patient’s hospital admission number were found a significant association with informal caregivers’ depression. Conclusion: This study finding will improve the quality of life and reduce the depression of caregivers of cancer patients by providing awareness through health campaigns. It is also important for treatment adherence, decreased hospitalization, reduced burden and treatment cost of caregivers.