The effects of some environmental factors on the degradation of cypermethrin by Klebsiella oxytoca were studied by Plackett-Burman design.Three major factors influencing the degradation were determined to be pH,temperature and inoculum volume.Moreover,its degradation condition was optimized by Box-Behnken design and response surface methodology.The optimum condition for degrading cypermethrin was that the strain was incubated in 30 mL mineral medium with 200 mg/L of cypermethrin,5.8 % of inoculum volume and pH 6.8 in 250 mL conical flask on a rotary shaker(180 r/min)at 33 ℃ for 120 h.Under this fermentation condition,the cypermethrin-degrading rate reached 84.67 %.