An aerobic and Gram-stain-negative bacterial strain, designated UKS-15T, was isolated from lake water in the Republic of Korea. Results of 16S rRNA gene sequence and phylogenetic analyses indicated that the novel isolate belongs to the genus Lysobacter and was most closely related to Lysobacter xinjiangensis RCML-52T (98.0 %), Lysobacter mobilis 9 NM-14T (97.4 %) and Lysobacter humi FJY8T (97.2 %). The DNA G+C content was 69.1 mol%. Strain UKS-15T possessed ubiquinone-8 (Q-8) as the sole respiratory quinone and the fatty acid profile comprised iso-C15 : 0, iso-C17 : 0 and summed feature 9 (iso-C17 : 1 ω9c and/or C16 : 0 10-methyl) as its major components. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and one unidentified aminophospholipid. Moreover, the physiological and biochemical results and low level of DNA–DNA relatedness (<22.0 %) allowed the phenotypic and genotypic differentiation of strain UKS-15T from other Lysobacter species. Therefore, on the basis of the data from this polyphasic taxonomic study, strain UKS-15T should represent a novel species of the genus Lysobacter , for which the name Lysobacter lacus sp. nov. is proposed. The type strain is UKS-15T (=JCM 30983T=KACC 18719T).