The objective of this study was to evaluate the effectiveness of different antibiotics against mastitis causing microorganisms in lactating dairy sheep in farm of east Slovakia. Milk samples from individual halves were cultured and bacteriologically evaluated. All the bacteria isolated through microbiological procedures were subjected to antimicrobial susceptibility test by disc diffusion method to a large number of antibiotics. The results revealed higher sensitivity against Amoxicillin (100% Coagulase Negative Staphylococci (CNS)). Medium level of resistance was observed against ampicillin (10.7%), cloxacillin (11.7%), oxacillin (10.7%) and penicillin (11.7%).