After short period of storage the coconut oil at room temperature we found that it becomes rancid. The oxidizing flavor is disgusting and causes economic loss. Some chemicals are used to prevent the oxidation of coconut oil but they are expensive and may be harmful to consumer’s health if used daily. Moreover, they are not suitable for homemade coconut oil and residual waste from the process may be environmental toxic. The present work thus aims at extracting substances from local plants and used as antioxidant for coconut oil. Seven kinds of local Caesalpiniaceae plants in Eastern Thailand namely Tamarind (Tamaridus indica L.), Peacock flower Caesalpinia pulcherrima L.), Flame tree (Delonix regia L.), Golden shower (Cassia fistula L.), Siamese cassia (C. siamea Lamk.), Candelabra bush (C. occidentalis L.), and Copper pod (Peltophorum pterocarpum DC.) were used. Ten grams of seed coats were mixed with 50 ml of the distilled water and 95% Ethyl alcohol (1:1) mixture in a closed container. The mixture was heated in a water-bath at 60 ℃ for about 2 hrs. and then kept in 10 ℃ icebox about 2 hrs. The mixture was then filtered and the filtrate was heated in an hot-air oven at 80 ℃ for about ? hrs. Ten ml of coconut oil was added with 0.5g of the extracts and kept at room temperature for 5 days. The pH and peroxide value (using the Iodometric titration method) of the oil were measured. It was found that the coconut oil with the Tamarind seed extract had the lowest peroxide value and was selected. Next the suitable amount of the Tamarind extract was studied by adding the extract to 10 ml coconut oil at 0-7% (w/v) and the contents were kept at room temperature for 5 days. The result showed that the 3% (and more over) Tamarind extract had the lowest peroxide value. Then the coconut oil with 3% Tamarind extract was kept at room temperature for 30 days. The pH and peroxide value were measured every 5 days. It was found that the oil could be stored for 25 days without significant change in pH and its peroxide value was less than 10 milliequivale n t oxygen per kilogram oil according to FAO/WHO (Codex) standard .Therefore, Tamarind seed coat at 3% could be used to retard the coconut oil oxidation for 25 days. This work presents the applicable use of plentiful local plants such as Tamarind seed, which is normally discarded, as an antioxidant for coconut oil.