Abstract: Four rumen and duodenum cannulated, Holstein lactating cows were used in a change-over design to determine the effects of NaOH, Formaldehyde or Urea treated barley on disappearance of Dry Matter (DM), Crude Protein (CP), Amino Acids (AA), NDF, ADF, hemicelluloses and starch in rumen, Post Abomasal Tract (PAT) and total tract by mobile nylon bag technique. Experimental treatments were coarse milled barley, barley treated with 3.5% NaOH, barley treated with 0.4% formaldehyde and barley treated with 3.5% urea that all chemical treated barley milled coarse before feeding. NaOH Treatment reduced concentrations of Lysine and Cystine in the barley grain. All chemical treatments decreased rumen disappearances of barley CP but only NaOH and Formaldehyde treatments also decrease total AA and some of the AA disappearances in the rumen. All chemical treatments increased DM, OM, CP, starch, NDF, ADF and hemicellulose disappearance of barley in the PAT. But only NaOH and Formaldehyde treatments increased total AA and most of AA disappearances in the PAT. Effect of chemical treatments on increase of disappearance of starch, Met and Gly in the total tract was significant (p<0.05). Rumen disappearance of TAA was lower than CP but PAT disappearance of TAA was more than CP and finally total tract disappearance of TAA was more than CP. Individual AA in barley disappeared at different rates in the rumen and PAT. Consequently, the proportion of digesta CP and AA entering the intestine must be considered.