Introduction: The main problem in poultry farming is the difficulty in producing food of animal origin without using antibacterial agents. Because most antibacterial compounds are dispensed in water, some water supply systems can be contaminated by antibiotics which are then administered to the animals unintentionally. This can lead to unexpected increases in antibiotic residues in food of animal origin. The aim of the present study was to determine whether the constant exposure of chicken broilers to enrofloxacin affects the withdrawal time of a therapeutic doxycycline that is intentionally administered to the chickens. Material and Methods: The concentrations of doxycycline, enrofloxacin, and ciprofloxacin were determined by LC-MS/MS in muscles and liver of the chickens. Results: Doxycycline residue concentrations in the chicken tissues from the group that received trace amounts of enrofloxacin were nearly 50% greater than those of the group that received only doxycycline. Conclusion: These results indicated that constant exposure to enrofloxacin in trace amounts significantly influences the residual doxycycline concentration in chicken tissues.