Pathology caused by S. aureus in poultry remain a matter of much concern for poultry industry. In the present article we study certain aspects of infection, experimentally induced in chickens with Staphylococcus aureus, namely methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA) and of its treatment. Chickens of Hisex Brown cross were challenged by intraperitoneal injection of Staphylococcus aureus in suspension at a dose 3.0 x 10^8 CFUs / 0.5 mL (2 McFarland/0.5 mL). The reliable data that we obtained show that the clinical signs of staphylococcosis develop in chickens 24 hours sooner on the average when the chickens have been challenged with MRSA than after the challenge with MSSA. In the former case the clinical signs are more severe and result in the death of model animals much more often. We studied the effectiveness of some antimicrobials such as lincomycin, enrofloxacin and levofloxacin, administered via drinking water at a concentration 300 mg/L, for treatment of chickens, challenged with S. aureus with different susceptibility to the aforementioned drugs. We proved that lincomycin, enrofloxacin and levofloxacin, administered via drinking water at a concentration 300 mg/L, for treatment of chickens, challenged with MRSA, have low effectiveness. Accordingly, the mortality rate for the chickens, treated with enrofloxacin was as high as 84%, lincomycin – 76% and levofloxacin – 56%. And on the contrary, the treatment of experimental staphylococcosis, caused by the isolate, susceptible to the above-mentioned drugs, led to much better results. Remarkably high effectiveness was achieved when we administered enrofloxacin (92%). The effectiveness was a little lower in the cases of lincomycin and levofloxacin (76%).