The importance of the diterpenic and rosmarinic acid content in the biological activities of rosemary extracts has been studied previously, but how the relationship between the concentration of these components affects their antioxidant and antibacterial activities has received little attention. Accordingly, from a total of 150 plants, 27 methanolic extracts were selected, for their similar diterpene contents but different ratios between carnosic acid and carnosol concentrations. In extracts with similar rosmarinic acid contents but differing proportions between carnosic acid and carnosol, the two diterpenes were seen to equally affect the in vitro antioxidant activity; however, and related with the antibacterial efficiency, this biological activity improved when carnosol was the major diterpene component.