Abstract: Plant extracts have been used for centuries for various purposes (e.g., traditional medicine, industrial applications, food preservatives) due to their antimicrobial properties and because most of them are categorized as Generally Recognized as Safe (GRAS) for human consumption. The main purpose of ruminant nutritionists is to manipulate the ruminal microbial ecosystems to improve the efficiency of converting feed to animal products. The use of feed additives such as antibiotics has proven to be a useful tool to reduce energy losses (in the form of methane) and nitrogen (in the form of ammonia). Reported that garlic (Allium sativum) have many biological activities, such as protective roles in cardiovascular function, as antihypertensive. garlic can have positive effects on the performance of different animals. Garlic has various properties including improve nutrient digestibility, antimicrobial, anti-inflammatory, anti-oxidant and immunostimulant in animal's nutrition. Thus, this review has discussed the effects of garlic in ruminants.