Phenol degradation has been carried out using commercial formulation of effective microorganism (EM-1) containing a mixture of Lactobacillus plantarum (1.0x10(4) C-FU/mL), Candida utilis (1.0x10(5) CFU/mL), Actinomycetes (3.5x10(3) CFU/mL), Streptomyces albus (3.0x10(3) CFU/mL) and Aspergillus oryzae (1.1x10(5) CFU/mL). Response surface methodology (RSM) has been adopted to evaluate the effect of different parameters such as initial phenol concentration, temperature, pH and time on phenol degradation. The maximum of 90.5% phenol degradation is observed at optimized value of process variables such as initial phenol concentration 1008 mg/L, temperature 35.5 degrees C, pH 7, incubation time 97.07 h. The R-2=0.997, adjusted R-2=0.9960 and predicted R-2=0.9890 values show that the experimental values are in good agreement with predicted values. The RSM is found to be useful in optimizing and determining the interaction among process variables in phenol degradation.