Bacteriological examination was carried out on 95 fecal samples and 95 nasal swabs collected from buffalo calves suffered from diarrhea and respiratory manifestation as well as 50 apparently healthy buffalo calves aged from | day up to 2 months old. The obtained results revealed the isoIation of 6 strains of Klebsiella species from healthy buffalo calves while 14 isolates of Klebsiella sp. were recovered from buffalo calves suffered from respiratory manifestation and 18 isolates from diarrhoeic buffalo calves. All isolates were identified as K. pneumoniae subsp pneumoniae , K. pneumoniae subsp ozaenae and K.oxytoca. The pathogenicity and virulence of different Klebsiella isolates were studied in mice. The study proved that Klebsiella isolates causing mortality rates ranged from 30% up to 80% after intramuscular , subcutaneous and oral routes of infection in mice and death occur usually between day 4 and 21 post infection. This study suggested that the use of ELISA for detection of antibody titre in mice using LPS as coated antigen revealed its efficacy in detection of klebsiella infection and cross reactions and it was highly sensitive and specific enough for extensive evaluation in the field.