A Gram-staining-negative, rod-shaped, non-spore-forming bacterium isolated as a contaminant from a biopharmaceutical process (strain CCUG 53591(T)) was studied for its taxonomic allocation. On the basis of 16S rRNA gene sequence similarity data, this strain was clearly allocated to the genus Herminiimonas. Herminiimonas saxobsidens was shown to be the most closely related species on the basis of 16S rRNA gene sequence similarity (99.9 %), followed by Herminiimonas glaciei (99.6 %) and Herminiimonas arsenicoxydans (98.8 %). Strain ND5, previously reported as H. glaciei, but showing 100 % 16S rRNA gene sequence similarity to strain CCUG 53591(T), was included in the comparative study. Similarities to all other species of the genus Herminiimonas were below 98.0 %. Chemotaxonomic data (major ubiquinone, Q-8; major polar lipids, phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol; and major fatty acids, C(17 : 0) cyclo, C(19 : 0) cyclo ω8c and C(16 : 0,) with C(10 : 0) 3-OH as hydroxylated fatty acid) supported the affiliation of the isolate to the genus Herminiimonas. DNA-DNA hybridization results (mean values) for strain CCUG 53591(T) with H. saxobsidens CCUG 59860(T) (34 %), H. glaciei DSM 21140(T) (57 %), H. arsenicoxydans DSM 17148(T) (17 %) and Herminiimonas fonticola S-94(T) (11 %) clearly supported the separate taxonomic position of this strain. Strain ND5 showed DNA-DNA similarities of 78, 56 and 52 % to strain CCUG 53591(T), H. glaciei DSM 21140(T) and H. saxobsidens CCUG 59860(T), respectively. Phenotypic differentiation of the isolate from the most closely related species was possible by various features. Hence, strain CCUG 53591(T) represents a novel species, for which the name Herminiimonas contaminans sp. nov. is proposed, with the type strain CCUG 53591(T) ( = CCM 7991(T)). Strain ND5 is a second strain of this species.