By means of topical application, fipronil resistance was surveyed in the rice stem borer, Chilo suppressalis,from 12 diferent areas in East China from 2001 to 2004. The rice stem borers in most regions of Jiangsu and Anhui were still susceptible to fipronil. But in Wuxi of Jiangsu and Cixi of Zhejiang, their sensitivity decreased (resistance ratios were 3.1 and 3.6), and the moderate level of resistance (resistance ratio was 21.2) was found in the population of Cangnan, Zhejiang. Therefore it was concluded that the pest resistant to fipronil was still at the early developmental stage. Synergism experiments showed that PBO had little effect on both susceptible and resistant borers (synergism ratios were 1.1 to 1.2). Though TPP and DEM had no effect on susceptible ones, they had significant synergism to fipronil in resistant borers (synergism ratios were 1.8 and 16, respectively), indicating esterase and GSTs might be involved in the resistance mechanism. Bioassay with currently used insecticides revealed that triazophos (because of high resistance), trichlorphon and acephate had very low toxicity to resistant borers, while diazinon, pyridaphenthion, decamethrin and avermectin showed high toxicity and had no cross resistance to fipronil, which could be considered as substitute insecticides in the resistance managment.