The study was designed to examine the effects of different manures (fish, pigeon and cow) and synthetic fertilizer (nitrogen) on some biochemical activities of Mentha piperita L. (mint, peppermint). Seventeen different phenolic constituents and 19 essential oils were determined in M. piperita samples. While caffeic, gallic, ferulic, protocatechuic, syringic, o-coumaric acids and rutin were detected as common phenolics; carvone, limonene and 1.8-cineol were identified as major essential oil components in all mints. Total phenolic compounds, ferric reducing antioxidant power and cupric (III) reducing capacity (CUPRAC) tests were used to evaluate antioxidant capacities of the mints. The highest total phenolic compound (4.8 mg gallic acid equivalents/100 g) and antioxidant capacity (971 mM Fe(II)/mg; 823 mM Trolox /100 g) were observed in mints fertilized with pigeon manure. Mint samples also had different antimicrobial activities against the studied microorganisms (eight bacteria and two fungi), especially Escherichia coli and Listeria monocytogenes.