Abstract: To clarify the difference in the absorption of ery thromycin base(EM) from varied intestinal segments, the absorption and intestinal wall permeability were investigated using in situperfusion method in the rat. Compared with other segments, significent higher percentage of EM disappeared from duodenum after it was perfused at same concentration for 2 hours. It is indicated that the duodenum was the best segment for EM absorption from rat intestine. The mechanism of EM absorption from intestine was investigated at different concentrations. When the concentration was raised from 0. 05 to 2.0 mg /ml, the uptake of EM increased and did not appear saturable, whereras the permeability cofficience was kept at an equilibrium level. Those indicated that the absorption of EM by intestine is majorly via passive transport mechanism.