Phthalate esters (PAEs) have a wide variety of industrial, agricultural and domestic applications, but the most important are their use as non-reactive plasticisers for improving the flexibility and workability of polymeric materials. PAEs are often discharged front the manufacturing processes into the environment and have often been detected at relatively high levels in soil, sediments, and waters. Biodegradation is a critical process affecting the environmental fate of PAEs. The present study aimed to investigate the biodegradation kinetics of dimethylphthalate (DMP), diethylphthalate (DEP), di-n-butylphthalate (DnBP), diisobutylphthalate (DIBP), di-n-octylphthalate (DnOP), and di(2-ethylhexyl)phthalate (DEHP) by a novel bacterium, Pseudomonas fluoresences FS1 metabolized PAEs with a new pathway, isolated from activated sludge at a petrochemical factory which has the ability to utilize PAEs as the sole source of carbon and energy under aerobic conditions. The optimum biodegradation temperature, pH, inoculum age and inoculum concentrations were 20-35 degreesC, 6.5-8.0, 18-24 h, 4-8% v/v. respectively. First-order kinetics was applied to the biodegradation DMP. DEP, DnBP, DIBP, DnOP, and DEHP by P. fluoresences FS1. The biodegradation rates of PAEs decreased and inhibition effects of PAEs increased greatly with increasing alkyl chain length and alkyl branch chains. (C) 2003 Elsevier Ltd. All rights reserved.