This study was conducted to investigate the effects of operational factors, namely: 1. type of activated sludge; 2. activated sludge concentration; 3. initial phenol concentration; and 4. addition of sucrose; on the biodegradation of phenol in batch experiments. At various initial phenol concentrations, complete phenol biodegradations with chemical oxygen demand (COD) removal of 95% were achieved by both unacclimated and phenol-acclimated activated sludge. The performance of biodegradation was greatly enhanced, with biodegradation time shortened from 330–1260 to 35–330 min for initial phenol concentrations of 25–250 mg l–1, when the activated sludge was acclimated to the target compound, despite the low acclimation concentration of 50 mg l–1. Phenol biodegradation time was found to decrease with increasing activated sludge concentration and decreasing initial phenol concentration. In the presence of sucrose as co-substrate, biodegradations of phenol by both unacclimated and phenol-acclimated activated sludge were improved. The kinetic data for the biodegradation of phenol was well-fitted into pseudo-first-order model. The values of rate constant of phenol-acclimated activated sludge were found to be higher compared to those of unacclimated activated sludge under all the operational conditions studied. For phenol-acclimated activated sludge, the values of pseudo-first-order rate constant, k, were observed to decrease with increasing concentration of activated sludge and decreasing initial phenol concentration.