Two Gram-stain-negative, facultatively anaerobic bacteria, designated ZY170218T and ZY180512, were isolated from lungs of dead sheep with hemorrhagic pneumonia in Yunnan Province, China and their taxonomic positions were studied by a polyphasic approach. The two isolates grew optimally at 37 °C, pH 9.0 and 1.0% NaCl (w/v), and showed identical 16S rRNA, recN and rpoB gene sequences. Phylogenetic analysis based on 16S rRNA gene sequence showed that the two strains fell within the cluster of species in the genus Mannheimia and formed a separated lineage with comparatively low similarity to the closest related species M. granulomatis (96.5%). Phylogenetic analysis based on rpoB gene indicated that the strains formed a monophyletic evolutionary lineage, with low sequence similarity ≤ 89.0% to the species of the genus Mannheimia. The genomic OrthoANI values between strain ZY170218T and M. granulomatis and M. haemolytica were 80.4% and 83.1%, respectively. The genomic G + C content of strain ZY170218T was 39.1 mol%. The predominant fatty acids (> 5%) of the two strains were C16:0, C14:0, C18:1ω7c, summed feature 3 (C16:1 ω7c and/ or C16:1ω6c) and summed feature 2 (C14:0 3OH/ C16:1 Iso). The major polar lipids of strain ZY170218T were phosphatidylglycerol, phosphatidylcholine, monogalactosyldiacylglycerol, bis(monoacylglycero)phosphate and diacylglycerols. The sole respiratory quinone of the two strains was CoQ-7. On the basis of phylogenetic, phenotypic and chemotaxonomic features, strain ZY170218T and ZY180512 clearly represents a novel species of the genus Mannheimia, for which the name Mannheimia ovis sp. nov. is proposed. The type strain is ZY170218T (= CGMCC 1.13620 T = KCTC 15731 T).