The research objective is to analyse the cost by the application of Activity-Based Costing of the cancer treatment process at a Thai public hospital by comparing the cost of cancer treatment with the compensation received from the National Health Security Office to set sustainability policy. Historical data were collected from 698, 295 and 348 cases of patients with breast cancer, liver cancer and colorectal cancer, respectively, from 1 October 2017 to 30 September 2018 by creating a matrix of coefficients and constants.The results showed that the cost of breast cancer treatment included the costs of 5 activities: breast cancer surgery, radiation, chemotherapy, the use of anti-hormone drugs and the treatment at the targeted cancer. The costs for the treatment of liver cancer included the costs of 5 activities: liver cancer surgery, TACE, radiation, chemotherapy and the treatment at the targeted cancer.And the cost of the treatment of colorectal cancer included the costs of 3 activities: colon cancer surgery, radiation and the use of chemotherapy.The treatments were found that the cost calculated from the activity-based were higher than the compensation received from the National Health Security Office. The research data constitute useful information for executives involved in policy makingabout managing and resources allocation to be the most appropriate and cost-effectiveness for sustainability of public hospitals in Thailand.