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Dissemination of multidrug-resistant, particularly tigecycline-resistant, <i>Acinetobacter baumannii</i> is of critical importance, as tigecycline is considered a last-line antibiotic. Acquisition of <i>tet</i>(X), a tigecycline-inactivating enzyme mostly found in strains of animal origin, imparts tigecycline resistance to <i>A. baumannii</i>. Herein, we investigated the presence of <i>tet</i>(X) variants among 228 tigecycline-non-susceptible <i>A. baumannii</i> isolates from patients at a Taiwanese hospital via polymerase chain reaction using a newly designed universal primer pair. Seven strains (3%) carrying <i>tet</i>(X)-like genes were subjected to whole genome sequencing, revealing high DNA identity. Phylogenetic analysis based on the PFGE profile clustered the seven strains in a clade, which were thus considered outbreak strains. These strains, which were found to co-harbor the chromosome-encoded <i>tet</i>(X6) and the plasmid-encoded <i>bla</i>_OXA-72 genes, showed a distinct genotype with an uncommon sequence type (Oxford ST793/Pasteur ST723) and a new capsular type (KL129). In conclusion, we identified an outbreak clone co-carrying <i>tet</i>(X6) and <i>bla</i>_OXA-72 among a group of clinical <i>A. baumannii</i> isolates in Taiwan. To the best of our knowledge, this is the first description of <i>tet</i>(X6) in humans and the first report of a <i>tet</i>(X)-like gene in Taiwan. These findings identify the risk for the spread of <i>tet</i>(X6)-carrying tigecycline- and carbapenem-resistant <i>A. baumannii</i> in human healthcare settings.