The purposes of this research were to 1) study activity-based costs of oil palm plantation in Nakorn Si Thammarat, and 2) to provide suggestions for cost reduction in oil palm plantation. Questionnaires were used to collect data from 393 palm oil farmers. The findings were obtained through studying the cost of each activity versus age range, and identifying the value-added activities and non-value-added activities. According to the results of this study, the average cost of the five plantation activities through all four age ranges was 148,354 Baht per Rai, and the highest cost activities were the harvesting activities and transporting activities, particularly of the 6-15 year-old oil palms. Furthermore, the findings suggested the farmers to omit some non-value-added activities, including the replanting activities and pest control activities, which had relatively small impact on the product quantity. To sum up, the cost and time required in the plantation will definitely be reduced, when these non-value-added activities are omitted from the entire process.