A new helical, alkaliphilic, gram-negative, chemoorganotrophic bacterium designated strain Z4T was isolated from Haoji soda lake in Inner Mongolia Autonomous Region, China. The isolate grows at salinities between 0.2% and 5.0% (w/v) NaCl and pH range 7.0-11.0, with an optimum at 2.0% (w/v) NaCl and pH 9.5. Its growth temperature ranges from 8 degrees to 49 degrees C with an optimum at 37 degrees C. The G+C content of the DNA is 46.8 mol%. The major isoprenoid quinone is ubiquinone 8 (Q-8). Phylogenetic analyses based on 16S rDNA sequence comparison indicates that strain Z4T is a member of the genus Marinospirillum. Phenotypic features and DNA-DNA homology of less than 20% with the described species of Marinospirillum support the view that strain Z4T represents a new species of the genus Marinospirillum. Strain Z4T (= AS 1.2746) is proposed as the type strain of a new species, named Marinospirillum alkaliphilum sp. nov.