As with other animal species, one of the most important challenges encountered in racehorse breeding is performance and economic losses caused by infectious diseases. Antibiotics are the most important and common drugs used for 2 2 protection against infectious diseases. Recently with the occurrence of antibiotic resistance, serious complications have emerged in terms of human and animal health.For this reason, to determine antibiotic resistance in bacteria, many research studies have been carried out in the world and Turkey. However, in Turkey no comprehensive study has yet been conducted on antibiotic resistance in racehorses. Within the scope of this study, it was aimed to investigate antibacterial susceptibility and resistance in Streptococcus spp. and Staphylococcus spp agents identified through isolation from tracheal aspiration fluid samples taken from thoroughbred horses brought to 75. Yıl Hippodrome Hospital. Disk Diffusion and Minimum Inhibitory Concentration (MIC) tests were used to determine antibacterial susceptibility. Susceptibility profiles of identified strains against some penicillin, cephalosporin, aminoglycoside, tetracycline, rifamycin and carbapenem group antibacterial drugs were determined. Also, it has been determined that 1 Streptococcus spp. and 10 Staphylococcus spp. agents are sensitive to amoxicillin and ampicillin-sulbactam; moderately sensitive to penicillin and amikacin and resistant to trimethoprim-sulfamethoxazole, kanamycin, gentamicin, enrofloxacin and rifampin.