The improvement in the growth of birds through the use of antibiotics could be obtained by reducing the count of harmful microorganisms, providing beneficial ones by suitable growth media, decreasing the thickness of gut mucosa and regulating the motility of gut, leading to better absorption of nutrients. However, achieving these desirable goals is not devoid of risks. Where, the frequent and improper use of antibiotics can reverse their therapeutic advantages through giving the opportunity to any existent microorganism to develop antibiotic resistance, which can hinder the effectiveness of antibiotics as chemotherapeutic or prophylactic agents in poultry. Additionally, antibiotic resistance genes can be transmitted to the natural environment and contaminate soil, water and plants. Moreover, the indiscriminate application of antibiotics could result in the accumulation of noticeable amounts of drug residues (the parent compounds or their injurious metabolites) in the edible tissues of poultry, including eggs and meat, which are very important sources in human feeding. The residues of antibiotics in poultry products can result in various pathological conditions and hazardous impacts on human health, such as being sensitive to antimicrobials in addition to allergy, cell mutations, imbalanced microbiota in the intestine and the development of bacteria resistance to antibiotics. This chapter describes the benefits and the hazards of using antibiotics as growth promoters in poultry feeding.