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 acetamip...