The aim of this study was to investigate the influence of aqueous extracts from the leaves of peppermint (Mentha ×piperita L.) on the seedlings and plants of common sunflower (Helianthus annuus L.). Different concentration of peppermint leaves extract: 1, 3, 5, 10, 15% was used to examine the growth (length), fresh and dry mass of common sunflower seedlings and plants watered peppermint extracts in phase of growth. We measured the length of seedlings and separated organs of plant: root, hypocotyl, epicotyl, petioles of the first row and remainder of he shoot. Additionally, we determined fresh and dry mass of these organs and cotyledons, leaves of the first order and remainder of the leaves. Depending on the concentration the aqueous extracts showed a stimulatory (low extract concentration) or inhibitory (high extract concentration) effect on growth, fresh and dry mass of common sunflower seedlings and plants.