The biodegradation of phenol, p-cresol, and phenol plus p-cresol mixtures was evaluated using Pseudomonas putida ATCC 17484 in aerobic batch reactors. Shake-flask experiments were performed separately using growth medium with initial nominal concentrations of phenol (50−600 mg L−1) and p-cresol (50−600 mg L−1) as well as phenol (50−600 mg L−1) plus p-cresol (50−600 mg L−1). The complete degradation of phenol and p-cresol was achieved within 48 h and 48−56 h, respectively, for all initial concentrations of phenol and p-cresol. The maximum cell growth rate using phenol (μmax,P = 0.45 h−1) was much faster than that using p-cresol (μmax,C = 0.185−1 h). The larger Ki value for phenol (310.5 mg L−1) revealed that the P. putida cells had a higher resistance to phenol inhibition compared with p-cresol (243.56 mg L−1). A mixture of phenol and p-cresol in batch experiments resulted in the complete removal of phenol within 52−56 h for initial phenol concentrations of 50−500 mg L−1. The time needed to remove p-cresol completely was 48−56 h for initial p-cresol concentrations of 50−500 mg L−1. In the continuous-flow immobilized cells reactor, the degradation efficiency for phenol and p-cresol was 97.6 and 89.1%, respectively, at a stable condition.