Bacteriological examination was carried out on Faeces of 119 buffalo-calves delivered from 99 Vaccinated and 20 unvaccinated buffalo-dams. The fecal samples were taken by rectal swabs From apparently healthy and diarrhoeic calves of Different ages from 1 to 30 days. E. coli was the Predominant organism in comparison with other Gram negative enteric bacterial pathogens. The Results of the determination of K99 adhesive antigen among E. coli isolated from apparently hhealthy calves showed 0 % and 20% in calves Delivered from vaccinated and unvaccinated Dams, respectively while in case of diarrhoeic Calves the percentages were 50 % and 80 % in Calves born from vaccinated and unvaccinated Dams respectively. Regarding the detection of enterotoxin production in relation to the presence of K99 adhesive antigen, all the K99+ E. coli strains That were recovered from diarrhoeic calves delivered from vaccinated and unvaccinated dams Were positive for enterotoxigenic effect. The results of field application of Nobivac vaccine containing K99 adhesive antigen denoted significant Decrease in the percentage of diarrhoea to 5.05 %. In calves born from vaccinated dams, as compared to 40 % in calves delivered from unvaccinated dams. Serum samples were collected from The vaccinated and unvaccinated pregnant buffalo-dams and from their newly born calves as well As colostrum for detection and evaluation of K99 Antibodies by the use of solid phase ELISA. The K99 antibody titers in the sera of vaccinated and Unvaccinated pregnant buffalo-dams showed a Significant difference at P <0.05. The highest Mean titers were 5670, 5167, 10791 and 7946 at 2 Week and 4 week after the 1st dose, 2 week post- Boostering and 48 hours after parturition in the Vaccinated buffalo-dams while it reached to 1342,1267, 1426 and 1262 in the unvaccinated buffalo Dams, respectively. The mean colostral K99 anti-body titers of buffalo-dams during 24 hours after parturition reached to 16291 in vaccinated dams while it reached to 3051 in the unvaccinated dams. Furthermore, the K99 antibody titers in the sera of newly-born calves were differed signifi- cantly at P <0.05 and the mean antibody titers in- creased from 0 to 9250 and 7160 after 48 hours and one week, respectively. On the other hand, the K99 antibody levels appeared higher in the serum of calves delivered from vaccinated dams than in calves delivered from unvaccinated dams.