A yellowish-pigmented bacterial strain, designated as MQ-18, was isolated from a sample of activated sludge collected from a pharmaceutical factory in Zhejiang, China. The strain was characterized through a polyphasic taxonomy approach. 16S rRNA gene sequence analysis demonstrated that strain MQ-18 showed high similarities to Piscinibacter defluvii SH-1 (99.7 %) and Piscinibacter aquaticus IMCC1728 (98.4 %), thereby suggesting that it belongs to the genus Piscinibacter. The DNA-DNA relatedness values of this strain to strains SH-1 and IMCC1728 were only 35.4 and 33.3 %, respectively. Cells of MQ-18 were Gram-negative, aerobic, motile, rod-shaped and non-spore forming. This strain exhibited growth at 25-37 °C (optimum: 30 °C) in the presence of 0-3.0 % (w/v) NaCl (optimum, 0 % NaCl) and at pH 5.0-8.0 (pH 7.0). The predominant fatty acids were C12 : 0 (5.5 %), C16 : 0 (33.7 %), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c; 38.5 %), and summed feature 4 (anteiso-C17 : 1 B and/or iso C17 : 1 I; 11.6 %). The main quinone type was ubiquinone-8, and the major polyamines were cadaverine and putrescine. The major polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The DNA G+C content was 70.1 mol%. On the basis of its phylogenetic, phenotypic and physiological characteristics, strain MQ-18 is considered to represent a novel species of the genus Piscinibacter, for which the name Piscinibacter caeni sp. nov. is proposed. The type strain is MQ-18 (CCTCC AB 2017223=JCM 32138).