Antimicrobial resistance genes (ARGs) and the bacteria that harbor them are widely distributed in the environment, especially in surface water, sewage treatment plant effluent, soil, and animal waste. In this study, we isolated a KPC-2-producing Klebsiella pneumoniae strain (GSU10-3) from a sampling site in Tokyo Bay, Japan, near a wastewater treatment plant (WWTP) and determined its complete genome sequence. Strain GSU10-3 is resistant to most ß-lactam antibiotics and other antimicrobial agents (quinolones and aminoglycosides). This strain is classified as sequence type 11 (ST11), and a core genome phylogenetic analysis indicated that strain GSU10-3 is closely related to KPC-2-positive Chinese clinical isolates from 2011 to 2017 and is clearly distinct from strains isolated from the European Union (EU), United States, and other Asian countries. Strain GSU10-3 harbors four plasmids, including a blaKPC-2-positive plasmid, pGSU10-3-3 (66.2?kb), which is smaller than other blaKPC-2-positive plasmids and notably carries dual replicons (IncFII [pHN7A8] and IncN). Such downsizing and the presence of dual replicons may promote its maintenance and stable replication, contributing to its broad host range with low fitness costs. A second plasmid, pGSU10-3-1 (159.0?kb), an IncA/C2 replicon, carries a class 1 integron (containing intI1, dfrA12, aadA2, qacE?1, and sul1) with a high degree of similarity to a broad-host-range plasmid present in the family Enterobacteriaceae The plasmid pGSU10-3-2 (134.8?kb), an IncFII(K) replicon, carries the IS26-mediated ARGs [aac(6')Ib-cr,blaOXA-1, catB4 (truncated), and aac(3)-IId], tet(A), and a copper/arsenate resistance locus. GSU10-3 is the first nonclinical KPC-2-producing environmental Enterobacteriaceae isolate from Japan for which the whole genome has been sequenced.IMPORTANCE We isolated and determined the complete genome sequence of a KPC-2-producing K. pneumoniae strain from a sampling site in Tokyo Bay, Japan, near a wastewater treatment plant (WWTP). In Japan, the KPC type has been very rarely detected, while IMP is the most predominant type of carbapenemase in clinical carbapenemase-producing Enterobacteriaceae (CPE) isolates. Although laboratory testing thus far suggested that Japan may be virtually free of KPC-producing Enterobacteriaceae, we have detected it from effluent from a WWTP. Antimicrobial resistance (AMR) monitoring of WWTP effluent may contribute to the early detection of future AMR bacterial dissemination in clinical settings and communities; indeed, it will help illuminate the whole picture in which environmental contamination through WWTP effluent plays a part. Copyright © 2018 Sekizuka et al.