An aerobic, Gram-stain-negative, rod-shaped bacterium (designated strain CC-G9A(T)), motile by a polar-flagellum, was isolated from a hot spring water sample in Taiwan. Strain CC-G9A(T) could grow at 20-42 �XC, pH 6.0-10.0 and tolerate up to 7% (w/v) NaCl. The 16S rRNA gene sequence analysis of strain CC-G9A(T) showed pairwise sequence similarity to Pseudomonas mendocina LMG 1223(T) (97.7%), Pseudomonas alcaligenes ATCC 14909(T) (97.8 %), Pseudomonas alcaliphila DSM 17744(T) (97.8 %), Pseudomonas toyotomiensis JCM 15604(T) (97.6 %), Pseudomonas oleovorans subsp. lubricantis DSM 21016(T) (97.6 %) and Pseudomonas argentinensis BCRC 17807(T) (97.5 %), and lower sequence similarity to other species of the genus Pseudomonas. According to DNA-DNA association analysis, the relatedness of strain CC-G9A(T) to P. mendocina BCRC 10458(T), P. alcaliphila DSM 17744(T), P. alcaligenes BCRC 11893(T), P. oleovorans subsp. lubricantis DSM 21016(T), P. argentinensis BCRC 17807(T) and P. oleovorans subsp. oleovorans BCRC 11902 was 55.1��3.1, 13.7��1.5, 14.1��1.8, 58.5��1.1, 28.9��2.0 and 28.6��1.8 %, respectively. The evolutionary trees reconstructed based on 16S rRNA, gyrB and rpoB gene sequences revealed varying phylogenetic neighbourhoods of strain CC-G9A(T) with regard to the most closely related type strains. The predominant quinone system was ubiquinone (Q-9) and the DNA G+C content was 64.3��1.3 mol%. The major fatty acids were C10 : 0 3-OH, C12 : 0, C12 : 0 3-OH, C16 : 0 and summed features 3 and 8 consisting of C16 : 1�s7c/C16 : 1�s6c and C18 : 1�s7c/C18 : 1�s6c, respectively. The major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol. According to distinct phylogenetic, phenotypic and chemotaxonomic features, strain CC-G9A(T) is proposed to represent a novel species within the genus Pseudomonas for which the name Pseudomonas guguanensis sp. nov. is proposed. The type strain is CC-G9A(T) (= BCRC 80438(T) = JCM 18416(T)).