A denitrification baffled reactor (DnBR) was developed to treat p-Cresol-laden wastewater. The effects of different operational parameters including p-Cresol initial concentration, hydraulic retention time (HRT), COD/NO3-, salinity and nitrate-free influent were studied on biodegradation and COD removal of p-Cresol. The results show that complete degradation of 1000 mg/L p-Cresol could be reached at HRT of 24 h. Also, in this condition, corresponding COD and nitrate concentration (2500 mg/L for both) were decreased to about 83 mg/L and 4.5 mg N/L, respectively. There was not a significant failure in the performance of the bioreactor at HRT value of 4 h and nitrate removal rate of 1.65 kg N/m(3) d was reached. The highest dehydrogenase activity of the DnBR was 17.65 mu gTF/gVS d for organic loading rate (OLR) of 7.5 kgCOD/m(3) d. DnBR could tolerate salinity concentration of 10 g NaCl/L, however increasing of salinity from 10 to 20 g/L caused moderate failure in the reactor performance. The optimum COD/NO3- was 0.9. Microbial community was also investigated and PCR results revealed that Bacillus megaterium, Bacillus aryabhattai, and Bacillus cereus were the predominant bacteria in degradation and mineralization of p-Cresol. Accordingly, DnBR could be considered as a promising technique for biodegradation and COD removal of p-Cresol in wastewater.