The leaves of Rosmarinus officinalis (rosemary) were subjected to supercritical CO2 extraction (SFE). Different sources of variability, including location (Izmir, Canakkale and Mersin) and harvesting time (December, March, June and September), were considered. Among active constituents of rosemary, carnosic acid, carnosol and rosmarinic acid were analyzed by HPLC. Variability of the amounts of active constituents appears to be due to different geographical locations of growth and seasonal variations. The levels of the constituents were higher in the months of December 2003 and September 2004. In addition to this, 12 SFE extracts were screened for their radical-scavenging capacities and antioxidant activities by various in vitro assays, namely total phenol assay, DPPH radical-scavenging activity and trolox equivalent antioxidant capacity (TEAC). The results revealed excellent correlation (r = 0.97) between the HPLC and total phenol assay.