A light-yellow-coloured bacterium, designated strain 4T-6(T), was isolated from cotton waste compost in Korea. Cells of the strain were strictly aerobic, Gram-negative, motile (by means of single polar flagella) and rod-shaped. Optimal growth occurred at 30 degrees C and at pH 7.0-8.0. The major fatty acids were 11-methyl C(18 : 1)omega7c (23.8 %), C(18 : 1)omega7c (23.2 %), C(16 : 0) (19.8 %) and C(17 : 0) (14.8 %). The DNA G+C content was 67.5 mol%. A phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 4T-6(T) was a member of the genus Phenylobacterium, showing the highest sequence similarities with those of 'Phenylobacterium zucineum' HLK1 (98.8 %) and Phenylobacterium lituiforme DSM 14363(T) (98.4 %). However, the values for DNA-DNA relatedness between strain 4T-6(T) and 'P. zucineum' HLK1 and P. lituiforme DSM 14363(T) were 45 and 43 %, respectively. Phylogenetic characteristics, physiological properties and DNA-DNA hybridization data indicate that strain 4T-6(T) represents a novel species of the genus Phenylobacterium, for which the name Phenylobacterium composti sp. nov. is proposed. The type strain is 4T-6(T) (=KACC 12597(T)=DSM 19425(T)).