A novel integrated biological and electrochemical oxidation (BEO) process was proposed for the treatment of biorefractory pesticide wastewater with high toxicity. An acetamiprid solution of 1000 mg L-1 was used as the target pollutant. Its biodegradability in terms of biochemical oxygen demand in a 5-d test period (BOD5)/total organic carbon (TOC) was only 0.0057, presenting its high biorefractory property. In the BEO system with boron-doped diamond electrode (BDD), the value of BOD5/TOC was improved to 1.17 and the toxicity was reduced by 40% in 3 h, maintaining the activity of microorganisms on a biofilter at an appropriate level. The intermediates (mainly small molecule carboxylic acids) produced in the electrochemical process served as nutrients for the microorganisms and then were biodegraded, while the biodegradation of these intermediates further enhanced the electrochemical oxidation of the original pollutant. The synergy of electrochemical and biological processes improved the removal of acetamiprid and TOC with higher efficiency and lower energy consumption. For the same TOC removal, the mineralization current efficiency (MCE) in the BEO was at least 40% higher than that in a single electrochemical oxidation (EO), and the energy consumption was only 53.3 (kW h)/m(3) in the BEO in 5 h, which was 44.5% lower than that in the EO. The BEO technique is an efficient method for the treatment of highly concentrated and biorefractory wastewater.