Bacteremia due to Capnocytophaga sputigena occurred in a 4-year and 9-month-old Japanese girl patient with acute erythroblastic leukemia in Shinshu University Hospital, Japan. On her admission to the hospital, she had a temperature of 38.2 degrees C with canker sore. Prior to the commencement of chemotherapy, peripheral blood culture was carried out with the BacT/Alert 3D System ver. 4.00D (bioMerieux Japan Ltd., Tokyo, Japan) using both the PF and the SN bottles. At 48 hrs of incubation, the System showed the positive sign only in the anaerobic SN bottle for bacterial growth. The strain isolated from the SN bottle was morphologically, biochemically, and genetically characterized, and finally identified as Capnocytophaga sputigena. The causative Capnocytophaga sputigena isolate was found to be a beta-lactamase-producer demonstrating to possess cfxA3 gene. The gene responsible for the production of CfxA3-beta-lactamase was proved to be chromosome-encoded, by means of southern hybridization analysis. This was the first case of bacteremia caused by chromosome-encoded CfxA3-beta-lactamase-producing Capnocytophaga sputigena.