The present study was conducted to assess the chemical composition of Yellow Maca (Lepidium meyenii) and its biological activity on stallions following oral administration of hypocotyl powder. Maca was subjected to methanolic extraction and the chemical analysis was carried out by LC-MS-QTOF (liquid chromatography-mass spectrometry). Our results showed that Maca contains some effective antioxidants, a high percentage of glucosinolates, and other important components with a high antioxidant capacity. To evaluate the plant biological activity in stallions fed with Maca powder for 60 days, the redox status and some reproductive parameters were investigated. Blood and semen samples were collected at 0, 30, 60, and 90 days from the beginning of this study. Blood samples showed a decrease of the reactive oxygen metabolites, evaluated by d-ROMs test, and an increase of the antioxidant barrier in terms of biological antioxidant potential (BAP test), powerful oxidant capacity (OXY-Adsorbent test), and thiols evaluation (-SHp test). Furthermore, semen samples showed a positive trend during Maca administration in the following parameters: ejaculate volumes and sperm concentrations, total and progressive motility, and acrosome integrity.