Tendency of isolated bacteria from infections in abdominal surgery during the period from April 2006 to March 2007 were investigated in a multicenter study in Japan, and the following results were obtained. In this series, 474 strains including 23 strains of Candida spp. were isolated from 170 (75.2%) of 226 patients with surgical infections. Two hundred and twenty-six strains were isolated from primary infections, and 224 strains were isolated from postoperative infections. From primary infections, anaerobic Gram-negative bacteria were predominant, followed by aerobic Gram-negative bacteria, while from postoperative infections aerobic Gram-positive bacteria were predominant, followed by anaerobic Gram-negative bacteria. Among aerobic Gram-positive bacteria, the isolation rate of Staphylococcus spp. was higher from postoperative infections, while Enterococcus spp. was higher from primary infections. Among aerobic Gram-negative bacteria, Escherichia coli was the most predominantly isolated from primary infections, followed by Klebsiella pneumoniae, Enterobacter cloacae and Pseudomonas aeruginosa, in this order, and from postoperative infections, P. aeruginosa was the most predominantly isolated, followed by E. coli and E. cloacae. Among anaerobic Gram-negative bacteria, the isolation rate of Bilophila wadsworthia was the highest from primary infections, followed by Bacteroides fragilis and from postoperative infections, B. fragilis was most predominately isolated, followed by Bacteroides caccae, Bacteroides thetaiotaomicron and B. wadsworthia in this order. In this series, we noticed no methicillin-resistant Staphylococcus aureus, nor multidrug-resistant P. aeruginosa. There were three strains of methicillin-resistant coagulase-negative Staphylococcus aureus, but all of them had good susceptibilities against various anti-MRSA antibiotics. We should carefully follow up B. wadsworthia.