Aim and Background: Plant bioactive substances are a valuable source of various medicines that play an important role in human health. Increasing resistance to different antibiotics has increased the importance of using plant extracts as they have potential sources of antioxidants. Antioxidant compounds of plant origin can protect the body from damage caused by oxidative stress. Recently, the use of natural antioxidants derived from medicinal plants has had medicinal and medical applications. Comparison of the antioxidant activity and total phenolic compounds of Thuja orientalis leaf extracts isolated from the three heights (1, 2, and 3 meters) of Noshahr and Tehran.