The successful application of co-immobilized aerobic-anaerobic biomaes under limited aeration in wastewater treatment systems would eliminate the problems associated with the intermediatess mono-chlorol(MCP) and di-chlorophenol(DCP) accumulations. With low initial pentachlorophanol(PCP) concentration, all PCP could be completely removed under oxygen-limited strict anaerobic conditions, and the removal efficiencies with different initial headspace oxygen percentage(IHOP) were not obviously different from each other. While at high initial PCP concentration, under strictly anaerobic conditios PCP and their intermediates were dearly higher than hat under other conditions, and produced obvious accumulation, the highest PCP reduction was achieved by the system receiving 30 IHOP, oxygen-limited system also exhibited lower residual TOC concentration and lower concentration of metabolic intermediates MCP and DCP. These results suggested that under strictly anaerobic condition the reductive dechlodnation of low chlorinated compoonde became rate limiting in the reductive dechlorination pathway, less chlorinated compounds be more amenable to aerobic degradation, and the aerobes of outer layers could function under limited oxygen. The co-immobilized aerobic-anaerobic biomass for methanogenesis under limited-aeration for chlorophenol degradation might be an attractive and efficient alternative for the sequential anaeroblc/aerobic system to achieve mineralization of a broad range of recalcitrance highly chlorinated organics and low final TOC concentratiOns.