In order to find the most fitted biodegradation model, biodegradation models to the initial 4-chlorophenol concentrations were investigated and had been fitted by the linear regression. The degrading bacterium, EL-091S, was selected among phenol-degraders. The strain was identified with Pseudomows sp. from the result of taxonomical studies. The optimal condition for the biodegradation was as fellows: secondary carbon source, concentration of ammonium nitrate, temperature and pH were 200mg/l fructose, 600 mg/l, $30^{circ}C$ and 7.0 respectively. The highest degradation rate of the 4-chlorophenol was about 58% for 24 hours incubation on the optimal condition. Biodegradation kinetics model of 5 mg/l 4-Chlorophenol, 10 mg/l 4-chlorophenol and 50 mg/l 4-chlorophenol were fitted the zero order kinetics model, respectively. Key Words : 4-chlorophenol, Pseudomonas sp., zero order kinetics model.