Botanical medicine is an ancient medicine used by human beings for thousands of years. Recently, phytobiotics, which are phytochemical compounds derived from plants, are investigated and used widely in the veterinary field as an alternative feed additive to antibiotic growth promoters. Phytobiotic feed additives can be defined as plants-/herbs-derived products added to the feed in order to improve performance of animals. Phytobiotics include herbs (non-woody and non-persistent plants), spices (with a powerful scent or flavour) and essential oils. These phytobiotics conatin subsequent tens of active principles that are classified into six major bioactive chemicals: phenolic, organosulfur, nitrogen-containing compounds, phytosterols, alkaloids, and carotenoids. Each chemical class of phytobiotics has a mode of action; e.g. phenolic compounds or flavonoids as major active ingredients are identified as potential antimicrobial and antioxidant agents. Therefore, the growth promotion outcome induced by phytobiotic feed additives varies depending on the phytochemical mixture used and their active chemicals as well as their concentrations. This review highlights the mode of actions of various phytobiotics, and their beneficial effects on feed intake, gut health, immune system, blood picture and biochemical indices as well as visceral organs, and subsequently their final outcome as growth promoters in poultry nutrition.