S u m m a r yIntroduction: Thuja occidentalis 'Brabant' and T. occidentalis 'Smaragd' are widely planted as decoration in parks and as hedges in domestic gardens in Poland. Objective: The aim of the study was to determine the yield and the composition of essential oils from different parts of these cultivars. Methods: The essential oils were obtained by hydrodistillation, and then analyzed by GC/MS. Results: Over seventy compounds were identified. The oils from leaves, twigs with leaves and twigs without leaves of 'Brabant' variety contained mainly α-thujone (61.0-64.4%), β-thujone (10.4-10.7%) and fenchone (7.7-8.0%), whereas in the cone oil there were α-thujone (42.1%), sabinene (11.2%) and β-thujone (10.2%). The main constituents of the oil from leaves and twigs with leaves of 'Smaragd' variety were α-thujone (49.2-49.3%), beyerene (12.8-13.2%) and sabinene (8.9-9.3%). Conclusions: The yield and chemical composition of the essential oil of T. occidentalis depend on the variety and plant organ. The oil of 'Brabant' variety contained more thujones and less diterpenes in comparison with the oil of 'Smaragd' variety.