The presence of AlkylPhenols (APs) in aquatic systems is considered as one of the environmental concerns in recent decades which are generally used as surfactants. APs are endocrine disruptors and estrogen-mimicking, causing harmful effects such as feminization and carcinogenesis on aquatic environment and human health. The most commercially important APs are 4-NonylPhenol (4-NP) and 4-tert-OctylPhenol (4-t-OP). Moving bed biofilm reactor (MBBR), which combined attached and suspended growth advantages, is an advanced biological treatment process for municipal and industrial wastewaters that has drawn considerable attention from many researchers to remove toxic pollutants from wastewater. The aim of this research was to evaluate Bacterial activities and kinetic coefficients in the presence of APs. This study was carried out using laboratory-scale MBBR fed with synthetic wastewater containing 4-NP and 4-t-OP. The reactor was operated at different loads of chemical oxygen demand (COD) and APs and different hydraulic retention time (HRT). The respirometric technique was applied to investigate the effect of APs on heterotrophic and autotrophic activity and kinetic coefficients in biomass obtained from MBBR. Respirometric technique demonstrates a reliable tool in order to assess the biofilm kinetic coefficients and biomass viability to insert in the mathematical models. The calculated kinetic parameters were in the range of conventional and extended aeration activated sludge processes. The results demonstrate that APs have significant inhibitory effects on activity and growth rate of heterotrophic and autotrophic bacteria, heterotrophs have been less affected by the presence of 4-NP and 4-t-OP, and these compounds had greater inhibitory effects on autotrophic bacteria. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical industry Press. All rights reserved.