These studies were made to assess the present stage of resistance to antibiotics, incidence and transferability of R-factors against E. coli. From March to July 1987, 59 strains of E. coli were isolated from specimens of patients collected at university hospitals in Seoul, 64 strains from stools of domestic animals and 66 strains from drainages in Seoul. These specimens were tested for resistance to 12 kinds of antimicrobial agents by means of agar dilution method. Using Muller-Hinton agar for the assay of drug resistance and tryptic soy broth as propagating medium for conjugation. The strains of E. coli were found to be resistant to one or more antibiotics and were considered to be potential donors of R-plasmid. The resistant strains of E. coli isolated from patients, domestic animals and drainages were found to be 55(93%), 33(52%) and 31(47%), respectively. Resistance to Tc, Ap and Cb was the highest in those isolated from patients and drainages, and resistance to Tc, Cm and Sm was the highest in those isolated from domestic animals. In the transfer test of drug resistance by conjugation method, 17 strains (47%) isolated from patients, 15(54%) isolated from domestic animals and 15(56%) isolated from drainages showed positive results, transperable resistant plasmid molecules with variable range in each strain.