Actinomycete strain H9T was isolated from coastal sediment of the Jiao-Dong peninsula (near Tsingdao city) in China, and was identified by means of polyphasic taxonomy. The strain grew autotrophically on modified nitrifying medium and heterotrophically on Luria-Bertani medium, with NaCl ranging from 0 to 8% (w/v) (optimal growth at 3.5%). The 16S rRNA gene sequence similarities of strain H9T to members of the genus Pseudonocardia ranged from 93.0 to 97.5%, indicating that strain H9T was phylogenetically related to members of the genus Pseudonocardia. Strain H9T had type IV cell wall and type PIII phospholipid, and its major menaquinone was MK-8 (H4). DNA-DNA relatedness values between strain H9T and Pseudonocardia kongjuensis, Pseudonocardia autotrophica and Pseudonocardia compacta were 42, 13 and 11%, respectively. These results support the conclusion that H9T represents a novel species within the genus Pseudonocardia, for which the name Pseudonocardia ammonioxydans sp. nov. is proposed, with the type strain H9T (= CGMCC 4.1877T = JCM 12462T).