Phenolic compounds are hazardous pollutants that are toxic relatively at low concentrations. Accumulation of phenol creates toxicity both for flora and fauna. Because of its toxicity, there is a need to decontaminate the phenol-laden soils. Here, bioremediation is a very useful alternative to conventional clean-up methods. The aim of this work was to study the effect of inoculum size and the influence of pH on phenol degradation by Pseudomonas aeruginosa. Phenol was degraded rapidly at pH (6 to 9), but the maximum rate of phenol degradation by P. aeruginosa was at pH 7. In contrast, the phenol degradation at pH (6, 8, and 9) was significantly lower, although phenol was totally depleted. Phenol was degraded at every inoculum size tested (1-10% v/v) but the maximum rate of phenol degradation was observed at 5% v/v in batch experimental system. These results are useful to understand the physiological and biochemical properties of P. aeruginosa before its optimum use in environmental application and these data will assist in choosing the right phenol degrader for a changeable environment.