In order to enhance natural products value, Melissa officinalis (lemon balm) aerial part (leaves) has been studied in this work. Hence, the objective of this study is to determine the chemical composition of the studied plant polyphenols extracts using HPLC/DAD, as well as evaluate their flavonoid extracts' antioxidant and antimicrobial activities using DPPH• and disk diffusion methods, respectively. The results of phenols chemical composition showed the existence of two phenolic acids, five flavonic aglycones and six heterosides, while the biologic results of the plant flavonoid extracts exhibited the existence of a good antioxidant and antimicrobial activities.