Essential oils are scented liquids extracted from certain plants. While some are extracted from flowers and leaves, others come from the seeds, stalks and bark. These concentrated oils contain actual elements of the plant that are referred to as the plant's “essence.” Because particles of a specific plant are contained in the essence, each type of oil has distinctive chemical properties and characteristics. Essential oils are made up of three elements almost exclusively carbon, hydrogen and oxygen. In Thuja the most prominent constituents of the oil are thujone-isothujone, fenchone and camphor. The main components of all essential oils of leaves were determined as α-pinene, δ-3-carene, sabinene and cedrol. These plants contain plant phytoconstituents such as carbohydrates, alkaloids, glycosides, flavonoids, tannins, saponins and flavonoidic constituents are Rutin, Quercitrin, Quercetin, Amentoflavone. Active compounds produced during secondary vegetal metabolism are usually responsible for the biological properties (antimicrobial, antioxidant, antiviral activity etc.) of plant used for various purposes, including treatment of infectious diseases. This review highlights the some important phytoconstituents and biological properties of T. orientalis and T. occidentalis.