Antimicrobial resistance patterns of 913 clinical isolates of Bacteroides fragilis group organisms were monitored during an 8-year period in Korea. In general the resistance rates of the non-fragilis B. fragilis group species were higher than those of B. fragilis for all the drugs tested. The rate of resistance to clindamycin remarkably increased and those to some β-lactam drugs such as piperacillin and cefotaxime also increased. No isolates were found to be resistant to imipenem, metronidazole, or chloramphenicol. β-lactam and β-lactamase inhibitor combinations and cefoxitin were more active than the other β-lactams. Therefore, these agents may be considered when empirical selection of antimicrobial agents is required to treat severe anaerobic infections.