Antibiotics are drugs that designed to treat different infectious diseases. Over use of antibiotics in farm animals like poultry as food additive, not to stop illness but to encourage rapid growth will increase presence of drug residues in livestock products. The problem of drug residues develop drug resistance, changing the natural microflora of digestive system, increase incidence of allergy in susceptible individuals, direct toxicity and interference in meat fermentation technology products. One of the main causes of drug residues is violation of withdrawal time. As a result of that, drugs usually accumulated in kidney, liver, fat, muscle and other tissues. Materials and methods: In this study, by use of four plate test, presence of different antibiotics in ten broiler flocks of poultry, referred to Mashhad slaughter house have been investigated. 160 samples from breast muscle and liver tissue were collected. The samples prepared as a disk and individually placed into each plate. The plates containing Bacillus subtilis with pH 6, 7.2, 8 and the plates containing Micrococcus luteus were incubated at 30°C and 37°C respectively. All samples were evaluated after 24 hours. Result and conclusion: The results of this study have been shown that 18.75% of samples had antibiotic residues and 6.99% of samples were suspected. By use of Fischer exact test, comparison of herd’s samples was performed. In 30% of herds, the presence of antibiotic residue at least in one liver sample and in 80% of herds the presence of antibiotic residue at least in one meat sample were confirmed. It is concluded that, quantity of antibiotics use and their withdrawal time should be controlled more effectively in food animals.

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