Three highly alkaliphilic bacterial strains designated as A1^T, H1^T and B1^T were isolated from two highly alkaline springs at The Cedars, a terrestrial serpentinizing site. Cells from all strains were motile, Gram-negative and rod-shaped. Strains A1^T, H1^T and B1^T were mesophilic (optimum, 30 °C), highly alkaliphilic (optimum, pH 11) and facultatively autotrophic. Major cellular fatty acids were saturated and monounsaturated hexadecenoic and octadecanoic acids. The genome size of strains A1^T, H1^T and B1^T was 2574013, 2475906 and 2623236 bp, and the G+C content was 66.0, 66.2 and 66.1mol%, respectively. Analysis of the 16S rRNA genes showed the highest similarity to the genera Malikia (95.1–96.4%), Macromonas (93.0–93.6%) and Hydrogenophaga (93.0–96.6%) in the family Comamonadaceae. Phylogenetic analysis based on 16S rRNA gene and phylogenomic analysis based on core gene sequences revealed that the isolated strains diverged from the related species, forming a distinct branch. Average amino acid identity values of strains A1^T, H1^T and B1^T against the genomes of related members in this family were below 67%, which is below the suggested threshold for genera boundaries. Average nucleotide identity by blast values and digital DNA– DNA hybridization among the three strains were below 92.0 and 46.6% respectively, which are below the suggested thresholds for species boundaries. Based on phylogenetic, genomic and phenotypic characterization, we propose Serpentinimonas gen. nov., Serpentinimonas raichei sp. nov. (type strain A1^T=NBRC 111848^T=DSM 103917^T), Serpentinimonas barnesii sp. nov. (type strain H1^T= NBRC 111849^T=DSM 103920^T) and Serpentinimonas maccroryi sp. nov. (type strain B1^T=NBRC 111850^T=DSM 103919^T) belonging to the family Comamonadaceae. We have designated Serpentinimonas raichei the type species for the genus because it is the dominant species in The Cedars springs.