The aim of this research was to determine yield, chemical composition and antioxidant properties of extracts and essential oils of sage (Salvia officinalis L.) and rosemary (Rosmarinus officinalis L.) leaves harvested during the months of June to September 2004. The maximum essential oil yields in the leaves were observed during July (3.24%) in sage and during August (1.35%) in rosemary. The maximum extract yields were found in July (15.57%) for sage and in June (30.48%) for rosemary. The sage oil was characterized by the presence of main components: camphore (20.73-26.07%), alpha-thujone (13.84-21.96), 1,8-cineole (13.94-20.40%), beta-thujone (7.07-9.34%) and beta-caryophyllene (2.28-9.19%). Fourteen compounds of rosemary essential oil were identified and the main components were found as camphore (14.77-31.12%), 1,8-cineole (7.70-26.18%), alpha-pinene (3.53-9.75%) and borneole (5.07-13.03%). Antiradical activities of sage and rosemary essential oils were found as IC50=2492.84-6645.43 mu g ml(-1) and IC50=370.03-2812.50 mu g ml(-1), respectively. Antioxidant capacities were also 25.20-43.46 mg AAE g(-1) essential oil for sage and 18.53-37.95 mg AAE g(-1) essential oil for rosemary. Sage and rosemary essential oils distilled from the early season (June) harvested leaves had the highest antioxidant activity, expressed as low concentration providing 50% inhibition of antiradical activity and high levels antioxidant capacity. Total phenolic content was between 85.33-110.52 mg GAE g(-1) extract for sage and 94.29-104.44 mg GAE g(-1) extract for rosemary. It was the lowest in June and the highest July in both extracts. Both antiradical activities and antioxidant capacities changed significantly depending on the phase in the growing season.