The biovariability of Hypericum perforatum L. (St. John's Wort) grown wild in Calabria and Sardinia (Italy) was reported with the aim to characterize the species through the isolation, detection, and quantitative evaluations of chemical markers (hypericin, quercetin, rutin) by HPLC analysis. Antioxidant activity of the methanolic H. perforatum extracts showed that the Calabrian samples were more active than those from Sardinia. The antibacterial activity evidenced the best performance on the gram positive bacteria with a MIC value of 50 microg/mL. Moreover, antifungal activity of all the extracts was also tested which showed interesting results particularly on the phytopathogene fungus P. ultimum. The variability shown by the samples could be attributed to environmental factors such as chemical-physical properties, composition of the soil, geographical coordinate, altitude, and solar exposure. The phytochemical analysis and the biological activity data suggested a possible use of H. perforatum extracts in the alimentary, cosmetic, and pharmaceutical fields.