Abstract Objectives Epidemic spread of OXA-48-producing Klebsiella pneumoniae, mainly mediated by the transmission of a blaOXA-48-carrying plasmid, has threatened global health during the last decade. Since its introduction to Taiwan in 2013, OXA-48 has become the second most common carbapenemase. We described the transmission and evolution of an OXA-producing K. pneumoniae clone in a single hospital. Methods Twenty-two OXA-48 K. pneumoniae were isolated between October 2013 and December 2015. Comparative genomic analysis was performed based on the WGS data generated with Illumina and MinION techniques. Results Seventeen of the 22 OXA-48 K. pneumoniae that belonged to ST11, with the same capsular genotype, KL64, and differed from each other by seven or fewer SNPs, were considered outbreak strains. Eight of the 17 outbreak strains harboured a 65 499 bp blaOXA-48-carrying IncL plasmid (called pOXA48). pOXA48 was absent from the remaining nine strains. Instead, a 24.9 kb blaOXA-48-carrying plasmid fragment was integrated into a prophage region of their chromosomes. Transmission routes of the ST11_KL64 K. pneumoniae sublineages, which carried either pOXA48 or chromosomally integrated blaOXA-48, were reconstructed. Conclusions Clonal expansion of ST11_KL64 sublineages contributed to the nosocomial outbreak of OXA-48 K. pneumoniae. The chromosome-borne blaOXA-48 lineage emerged during a 2 year period in a single hospital. Dissemination of OXA-48, which is vertically transmitted in K. pneumoniae even in the absence of selective pressure from antimicrobials, deserves public health attention.