Serratia marcescens (S. marcescens) is considered an important opportunistic pathogen and has been found to be associated with outbreaks of mastitis among dairy ruminants. Like other various bacterial diseases, multidrug resistance strains pose a serious threat to public health and are considered a great obstacle during treatment of such field problems. The aim of this study was to investigate Serratia species, antimicrobial susceptibility, and presence of resistance genes of S. marcescens isolates associated with mastitis cases. Eighty mastitic milk samples were collected from different dairy farms located in Menoufia Province. S. marcescens was isolated and confirmed in 6 mastitis milk samples out of 80 (7.5%) using culturing and gram staining .VITEK 2 (bioMérieux) System was used to complete the identification  of S. marcescens. The cultured bacteria were then purified for detection of resistance gene. Further, the resistance of these isolates against antibiotics had been investigated by disk diffusion method and the findings revealed that the isolated strains are sensitive to some antibiotic as cefepime (6\6,100%), ceftazidime (5\6, 83.3%), cefotaxime (4\6, 66.6%), Amoxicillin-Clavulanic acid (6\6,100%), whereas wide differences were observed in the patterns of resistance among the bacterial isolates  in particular,  Ampicillin (6\6, 100%), chloramphenicol (5\6, % 83.3%), imipenem (4\6, 66.6%). Additionally, The results of resistance genes detection in S. marcescens revealed that the most prevalent resistant genes encodings β-Lactams were blaTEM (6\6,100%), bla CTX-M (6\6, 100%),CYM(CIT) (4 \6,66.6%) , genes encoding chloramphenicol floR (5\6, % 83.3%), and genes encoding carbapenemases bla IMP (6\6,100%), OXA (2\6, 33.3%), SME (2|6, 33.3%).