This antimicrobial resistance surveillance study was performed in 100 medical centers. Susceptibility testing (Etest; AB BIODISK, Solna, Sweden) of 9152 strains including Escherichia coli (991 strains), Klebsiella spp. (1000 strains), Enterobacter spp. (971 strains), Citrobacter spp. (803 strains), indole-positive Proteae spp. (834 strains), Serratia spp. (902 strains), Acinetobacter spp. (874 strains), Pseudomonas aeruginosa (992 strains), oxacillin-susceptible Staphylococcus aureus (984 strains), and coagulase-negative staphylococci (CoNS; 801 strains) was performed with 7 beta-lactams (cefepime, cefpirome, ceftazidime, cefoperazone/sulbactam, imipenem and piperacillin for Gram-negative bacteria, or oxacillin for Gram-positive bacteria). No strain resistance to these beta-lactams (except for ceftazidime) was found in oxacillin-susceptible S. aureus and CoNS. Of the E. coli clinical isolates, 17.1% were resistant to piperacillin, whereas 2.9% or less (cefpirome = 2.9%) were resistant to other beta-lactam agents. Klebsiella spp. strains were more susceptible to imipenem (99.9%), cefepime (99.2%), ceftazidime (98.6%), and cefpirome (98.3%). Isolates of Enterobacter spp., Citrobacter spp., indole-positive Proteae, and Serratia spp. were susceptible to imipenem, cefepime, and cefpirome as well. Acinetobacter spp. strains were least resistant to cefoperazone/sulbactam (0.7% resistance), imipenem (2.6%), cefepime (6.6%), and ceftazidime (7.7%) compared with other beta-lactam antibiotics tested. Isolates of P. aeruginosa were more susceptible to ceftazidime (8.7% resistance), cefoperazone/sulbactam (9.8%), and cefepime (8.9%) than piperacillin (11.9%), cefpirome (16.2%), and imipenem (12.4%). The percentage of imipenem-resistant P. aeruginosa was approximately 13% in clinical isolates in Japan. The proportion of strains resistant to beta-lactam antimicrobials has been decreasing compared with data from 2004, suggesting that reduced consumption of beta-lactams has reflected the decreased rates of resistant bacterial isolates in Japan.