Melissa officinalis L (lemon balm) is a traditional herbal medicine used widely as a mild sedative, spasmolytic and antibacterial agent. This paper focuses on the analysis of the chemical composition and the biological activities of M. officinalis essential oil obtained under controlled harvesting and drying conditions. An in-vitro cytotoxicity assay using MTT indicated that this oil was very effective against a series of human cancer cell lines (A549, MCF-7, Caco-2, HL-60, K562) and a mouse cell line (B16F10). This oil possessed antioxidant activity, as evidenced by reduction of 1,1-diphenyl-2-picryl-hydrazyl (DPPH). These results pointed to the potential use of M. officinalis essential oil as an antitumoral agent.