Effects of Bnk Ⅶ and Bmk ⅩⅢ from venom of the scoripion Buthus martensi karsch on spontaneous active potential of the central nerve of insects were investigated. Methods Using extracellular recording, we observed the effect of BmK Ⅶ and BmK ⅩⅢ on spontaneous active potential of the exposed central nerve cord of Periplaneta americana.Results We found that BmK Ⅶ (1 ug/mi) first exerted its reversible inhibition and then fol loved the excitation. BmK ⅩⅢ ( 10 ug/ml has only inhibiting effect, which is irreversible. Conclusion These results indicated that BmK Ⅶ is a mixture including inhibiting and exciting components, while BmK ⅩⅢ has only inhibiting component. The effect of these two toxins possibly through the modulation to sodium channels of the neurons.