A Study was conducted to investigate the effect of feeding Lactobacillus casei YS on the growing performance and gastrointestinal flora of the suckling piglets, which were delivered from 2 heads of three-way crossbred(Landrace$ imes$Large White$ imes$Duroc) pigs, for 4 weeks. The results from the present study was summarized as follows. Average body weight gains of feeding group was slightly better than that of control group and diarrhea was prevented by successive 7 days feeding. Population levels of lactic acid bacteria were maintained about 107 colony forming unit(cfu) per gram of the contents in both feeding and control group at upper parts of small intestine. In this part, coliform count was greatly reduced in (ceding group but not in control group. pH values of the intestinal contents were gradually decreased especially at the upper part of alimentary track of feeding group. Among lactic acid bacteria, L. salivarius, L. cases and L. fermentum were found most predominant strains in feeding group, Wheareas L. salivarius, L. acidophilus and L. cunts in control group. In the other hand, Escherichia coli recovered from scouring pigs were resistant to the drug such as streptomycin, ampicillin and sensitive to gentamycin and neomycin in vitro test.