A taxonomic study was carried out on a novel aerobic bacterial strain, designated CC-CY503(T), isolated from food-waste compost in Taiwan. Cells were Gram-stain-negative short rods, motile by means of a monopolar flagellum. Strain CC-CY503(T) was able to grow at 20-50 �XC and pH 6.0-10.0 and to tolerate <6% NaCl (w/v). Phylogenetic analysis of 16S rRNA gene sequences showed that this bacterium belonged to the genus Pseudomonas, with Pseudomonas pertucinogena ATCC 190(T) as the closest neighbour, sharing a sequence similarity of 97.9%. The DNA-DNA relatedness value of strain CC-CY503(T) with P. pertucinogena ATCC 190(T) was 37.8 �� 2.3%. The phylogenetic trees reconstructed based on gyrB and rpoB gene sequences supported the classification of strain CC-CY503(T) as a novel member of the genus Pseudomonas. The predominant quinone system was ubiquinone (Q-9) and the DNA G+C content was 63.1 �� 0.4 mol%. The major fatty acids were C(12:0), C(16:0), C(17:0) cyclo, C(19:0) cyclo �s8c and summed features 3 and 8 consisting of C(16:1)�s7c/C(16:1)�s6c and C(18:1)�s7c/C(18:1)�s6c, respectively. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and phosphatidylcholine. On the basis of its distinct phylogenetic, phenotypic and chemotaxonomic features, strain CC-CY503(T) (=BCRC 80437(T) =JCM 18415(T)) is proposed to represent a novel species within the genus Pseudomonas, for which the name Pseudomonas formosensis sp. nov. is proposed.