A novel anaerobic chemoorganotrophic, facultatively alkaliphilic bacterium (strain M17 DMB^T) was isolated from a coastal lake (Golubitsckoe, Taman Peninsula, Russia). Cells were motile rods, 1.6–2.1 µm long and 0.45 µm in diameter. The temperature range for growth was 14–42 °C, with an optimum at 30 °C. The pH range for growth was pH 5.5–10.0, with an optimum at pH 8.0–8.5. Growth of strain M17 DMB^T was observed at NaCl concentrations of 1–12 % (w/v) with optimum growth at 1.5–2.0 %. Strain M17 MB^Tutilized glucose, fructose, sucrose, ribose, mannose, raffinose, arabinose, dextrin, yeast extract, peptone, carbon monoxide, vanillic acid and 3,4-dimethoxybenzoic acid. The end products from glucose fermentation were acetate and ethanol. The DNA G+C content of strain M17 DMB^T was 39.1 mol%. The closest phylogenetic relative of strain M17 DMB^T was Alkalibacter saccharofermentans with 97.8 % 16S rRNA gene sequence similarity. The OrthoANI value between M17 DMB^T and A. saccharofermentans was 70.4 %. Based on the phenotypic, genotypic and phylogenetic characteristics of the isolate, strain M17 DMB^T is considered to represent a novel species of the genus Alkalibacter for which the name Alkalibacter mobilis sp. nov. is proposed. The type strain of Alkalibacter mobilis is M17 DMB^T (=KCTC 15920^T=VKM B-3408^T).