Klebsiella pneumoniae resistant to both carbapenem and colistin has become a major clinical challenge. Although such resistant isolates are rare, they have been sporadically reported from many areas of the world. To investigate the prevalence and resistant mechanisms to carbapenem-resistant, colistin-resistant K. pneumoniae among Korean patients, we selected these resistant K. pneumoniae from clinical isolates collected over a period of five years at a tertiary hospital in Jeonbuk, Korea. The minimum inhibitory concentration of a variety of antibiotics against the resistant isolates was determined by the macrodilution method or the E-test. PCR analysis was used to determine sequence types (STs) and identify the genes involved in resistance to carbapenem and colistin. In 338 K. pneumoniae clinical isolates, two exhibited both carbapenem and colistin resistance. The ST of these belonged to ST11 and ST258, the most prevalent STs with K. pneumoniae carbapenemases, but the isolates did not carry any prevalent carbapenem-hydrolyzing β-lactamase genes. The carbapenem resistance was mediated by loss of porins OmpK35 and/or OmpK36 associated with DHA-1 AmpC β-lactamase. The colistin resistance was caused by amino acid changes in PmrB, PmrC, PmrE, PmrK, and MgrB, including novel amino acid changes in PmrE and PmrK. We first reported novel carbapenem-resistant and colistin-resistant K. pneumoniae ST11 and ST258 with mutations within ompK35, ompK36, mgrB, and pmr genes in Korea. The results suggest that noncarbapenemase-producing carbapenem-resistant, colistin-resistant K. pneumoniae might be prevalent in Korea, and that better measures are necessary to control the spread of the resistant pathogen.