The purpose of this study was to evaluate effect of chitosan-oligosaccharides(CHIOL) on hydrophobicity of pathogenic E coli including a field isolate from suckling piglet with diarrhea, E coli-0157:H7, and E coli-O149:K88ac. E coli field isolate appeared adhesion of 100% to n-hexadecne between 0.00125% and 0.05% CHIOL. E coli-O157:H7 occurred adhesion of 69% and 64% under the level of 0.00125% and 0.025% CHIOL, respectively. E coli-O149:K88ac showed adhesion of 100% in higher than 0.025% CHIOL. For cationic action, the adhesion of E coli isolate and E coli-O149:K88ac to n-hexadecane were inhibited at level of higher than 10mM Ca2+ but did not induce any difference among the concentrations used(p0.01). However,the adhesion of E coli-O157:H7 to n-hexadecane was inhibited at level of higher than 50mM Ca2+. In a field trial, control piglets showed average mortality of up to 58% during 3 days after the onset of diarrhea. In contrast, the prevalence of E coli-induced diarrhea in CHIOL-treated groups without mortality was dropped down to average 34% on the 1st day after the treatment of CHIOL, and average 2% on the 4th day. After then, piglets with diarrhea was not present. In conclusion, the low concentrations of CHIOL were most likely to associate with the enhancement of hydrophobicit to pathogenic E coli. Calcium inhibited the hydrophobicity of E coli by CHIOL. These results suggested that CHIOL could be played an efficient and reliable role in treating enteric colibacillosis of piglets.